Any pokemon will come out of an egg an using Pokesav (put it in your box as an egg -> set steps to 1 > save it, load it and walk around) This method also helps bypass the legallity checker as long as the pokemon used doesn't have EVs higher than 510 (255 max per stat), IV's that aren't quite obviously hacked (I.E 31 in every stat) and moves that are not in the set move list . Obviously this method doesn't work for event only pokemon as they are non breedable (bar manaphy) and therefore couldn't have hatched from an egg.
Oh and another thing, for it too look legit you cant give it a trait that it doesn't have, and if hatched it has to be in a pokeball
Sorry if I completely danced around your original question there, but in short like someone above said 'Pokesav or Nothing' for the time being, I know of the guy that is currently working on something called PPRE which will allow you to edit how the pokemon evolve.
EDIT: You can also change evolution chains via Hex Editing. However I have never tried to hex edit ... anything lol so you'll have to look around for a tutorial on how to do so if you want to be able to do it
(Thanks to Roland for pointing that out to me

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