This is kind of like the idea I had about picking which episode that I and other fans would rewrite. Here I was thinking about doing the same to Equestria Girls. Whatever your opinion about this spin-off is, we can all agree that it isn't really perfect. I personally have a few things that I would change about this series, some of which are something I'm going back and forth on.

1. Every sapient creature in Equestria would be human in the human world. I do kind of like the idea of Spike and other dragons being dogs, but it does throw a wrench in the gears of how the portal works. While I have a headcanon about some creatures and what they would be in the human world, I think it would be much easier if we just had all the species (Ponies, Dragons, Griffons, etc.) all be humans.
2. Different outfits. I know that they eventually changed the wardrobes of the humane 7, but the first outfits they had in the first three movies did not look good. One of the best alternate designs I found was drawn by teammagix. I'll let you be the judge of what you think about this. Still, designs like this would be much better. Speaking of which...
3. Skin & Hair Colors. This is probably the most distracting part of Equestria Girls, or at least for me. For some reason, they chose to have the skin color of the humans be the same color as their pony counterparts. I don't fully understand this, but it's kind of distracting to me. Another change that's a big maybe for me would be the hair color. Without the multicolored hair, it would honestly be a little hard to tell who the characters would be.
4. Human Names. I kind of doubt that this would be something that would happen, but it's kind of worth something to think about. On a previous forum, Echo Nymph commented some names that would be fitting for the mane six and Spike if they were human. I even threw a couple of ideas for other characters. It's not something that would've been likely, but it certainly would've been a fun possibility.
5. Age. This one I'm a little more confident in. My guess for the mane six's age is that they're young adults, about their early twenties. However, in the human world, they're high school seniors. Still gives some good ideas for a plot, but I honestly think we could have more possibilities if they were young adults. If they were going to have as a plot point, why not use Spike? He's much younger than the mane six but still has shown he can have a good episode focusing on him. Twilight could've had Spike enrolled at the school to help get some more information about this world.

Anyways, these were some things that I would change about Equestria Girls. Do you agree with some of these ideas? Do you have any ideas that I didn't bring up?

7504394

1: I'll go with that. Spike being a dog seemed to only happen for plot reasons: Twilight wouldn't be able to hide Spike in her backpack if he was a human. Though since Twilight was more or less left alone and she wasn't really questioned about why she showed up, they probably could've handled things largely the same even if Spike was a human.

2: I didn't mind the outfits, but I did feel that at least some of the human mane 7's outfits didn't fit them. I would be good with a change and also have them all have outfits that stand out from each other, like how the newer ones do.

3: I always figured the human characters having the same skin color as their pony counterparts were partly meant to show they are somehow connected as well. I feel it's one of those changes that wouldn't help or hurt much. The hair I think should stay, especially if the skin color were to change.

4: For ease of being able to tell who are the mane 6's counterparts sooner, I think the names should stay the same, but it may be fun to think about what their names might be if the names are "humanized". I would particularly like this idea if it's more like a AU instead of a "rewrite" of EQG,

5: This one would partly depend on if I'm keeping the show's target audience the same, or if I'm treating things more like fanfiction and thus can throw that out the window, as well as anything else the show's writers and editors have to take into account that fanfic writers don't. Most main characters of showed aims at kids usually are kids or teens, and the pony mane 6's ages were always kept unknown, so they could be thought of as teenagers if someone wanted to. If I keep this new version of EQG's target audience the same, I'll keep the ages the same, but would just try to actually explain what the deal with the age-changing the portal does if I can.

If I'm doing an EQG rewrite more like rewrites are done in fanfiction, I may still keep the ages of the human mane 6 the same. But if I were to have ideas that would work if the mane 6 are adults and think it'll be better than the ones that can work with them as teens, I'll be for changing their ages.

7504394

Every sentient creature

It's 'sapient', not 'sentient'.

7504708
Right, I can fix it.

7504713
You're welcome.

7504474
Given how the CMC are freshmen, Spike's human form can easily be that too.
Or even older, especially since its clear Spike is older than he looks.

I feel like Megan's answer of "How would a little boy fit into the backpack" makes it sound like they just made him a dog because they wanted him in a backpack because its cute. More like absolutely stupid reason to make him a dog..
Her logic of "dragons are not ponies and thus not allowed to be humans" with the portal is really awful. And it got contradicted due to the Diamond DOGS being humans. That rule went out of the window for sure.

7505105
I have a feeling that the jokes are funny for the moment, but in the long run they end making things harder to understand. Basically, Spike is now stuck being a dog in Equestria Girls because of a couple of jokes.

7504394
Personally I'm fine with the technicolor-skinned humans, I think it makes the world a bit more colorful and lively. If anything, I find it weird that they didn't go all-in on this - it makes Big Mac feel like a rather strange outlier. (Admittedly, it's probably because a bright red human might look a bit odd even by the show's standards).

I also agree that human forms for all creatures travelling through the portal makes a lot more sense - although to be fair, this is a problem that is only known to affect Spike. However, I would have really liked a human Spike, which I think has a lot more potential than him being a dog. Still, at least they stuck to their guns on it.

My main issue with EQG is the lack of any real worldbuilding or consistency. It always felt to me like a golden opportunity was missed. EQG is about a human world; this should be a place more familiar and relatable to us than the magical pony world, yet somehow the opposite is true - it's Equestria that seems to have far greater consistency and relatability. And it's not like that's even a high bar to clear - FiM was hardly the most rigorous show when it came to continuity or world development.

With EQG, it should have been easier. There's no expansive magical kingdom or deep lore - it's just a human town full of human people. It wouldn't have been much trouble to add a bit of structure and solidity to this setting, but we really didn't get anything. We rarely, for example, get a sense of the society and community of EQG; what the social networks of the school look like, who knows who, etc. It's just the Humane Seven and Everyone Else, and those are the only two options. For a series based around a school, this feels hopelessly anemic. EQG1 didn't even try; it just asserted that the school is full of cliques and left it at that.

That works in pony because we generally are more invested in our main characters; we accept and even celebrate background ponies because we know they're not an essential part of the story being told. But that approach really didn't seem to work well for a human setting. I always found the background humans in EQG to be very alien. Who are they? What are they like? I have no idea; the show keeps them away from our main characters with a bargepole. In particular, I genuinely have never understood why these humans are not counterparts to background ponies, which made so much sense that not doing it comes off as conspicuous. Why go the the effort of creating something that has no presence?

Some geography would also have been nice. How big is Canterlot City? Who lives where? What are the landmarks? Where are things located? What towns are nearby? If Rarity has a freakout at home, which of her friends would reach her first? At least in FiM we can identify locations, even if the show isn't interested in nailing down any specific geography for them. With EQG, I've got no idea. There's a mall where everyone works, I guess, except Pinkie who works at a diner. Somewhere.

These questions are maybe beyond the scope of a kid's cartoon, but even a little would be nice, and they have done it before. In EQG1, there's a throwaway line in which Pinkie mentions that she knows Twilight's human counterpart and that she lives "in the city". This was not an insignificant piece of knowledge. At the least, it assured us there was something outside of the school, and it also indicated that Twilight does actually have a counterpart, which isn't a given considering that none of the weird background humans do. This single line of information also provided an amazing post-credits scene for Rainbow Rocks, and was even was picked up in the opening of Friendship Games, in which Sci-Twi jumps on a bus after scanning the portal - suggesting that she does, indeed, live somewhere far enough away that you can't easily walk there. It's such a bounty from such a trivial piece of worldbuiding. They could have done so much more.

7505339
They didn't really stick their guns due to they broken their so called logic of the portal making Spike a dog, by having Diamond DOGS be human.
Along with Spike's human-world counterpart being a dog in the first place. So its not the logic of the portal making him a dog due to he's not a portal but its due to the universe thinking its funny to reduce him to a lowly pet. So pretty much their in-universe attempt to justify why he's a dog got thrown out the window and essentially goes "Its because its funny he gets the short end of the stick"
Spike being the only one affected by it is extremely unfair for him since its like he's been singled out for the sake of a joke.
If other dragons were dogs, it will insult dragons in general by saying that are lower beings that ponies there. So its a lose-lose situation on if Spike is a dog.