I'd day no.

Personally, I'd argue that it depends on the author. Chimerism is the excuse I went with in my story, but there are definitely other options.

Off the top of my head, there's also genetic anomalies, alt-universe rules on pony hybridization, or, for those with a more sci-fi leaning, surgical grafting or clone fabrication procedures.

7871116
you would Day no

7871174

there's also genetic anomalies

that's how I go in my story

for those with a more sci-fi leaning, surgical grafting or clone fabrication procedures.

wouldn't that be this group
Chemically/Artificial made Alicorns

7871372
It depends on whether or not they are alicorns in the end.

The way I see it, grafting a horn and wings onto an earth pony or genetically modifying a pegasus clone to have earth traits and a unicorn horn or modifying a unicorn to have wings and earth traits would all be cases of chemically or artificially made alicorns. Adding a horn to a pegasus or wings to a unicorn without adding any earth traits would only make them artificial pegacorns.

That's just my perspective, at least.