If Celestia hates the Grand Galloping Gala that much, why doesn't she just change the way it works?

7081757
She doesn't hate it, she just finds it very boring since it hasn't changed in most of the time it's existed. Also there is probably a lot of tradition and reason behind the GGG that she just can't change on a whim.

7081757
There's no indication she hates the Gala, just that it can be dull. After all, she's seemed to have resigned herself to the position of greeting others. If she were to join others in the festivities, I'm sure she would think differently. It also appears to be something of a national holiday, or at least an event that captures the attention of the kingdom, so she probably wouldn't want to disappoint others by cancelling it. Standing around for a day and offering "hellos" isn't really that bad, it's just bound to get dull.

7081757 I've been wondering that since season one.

7081772 I find that hard to believe given that she's the ruler of Equestria. She can practically do anything she wants, within reason.