How to keep illegal abilities from changing upon evolution

[Meli]

I'm generating a bunch of eggs for an egglocke in black 2 & I want to give the mons illegal abilities. During playtests I've noticed that they change back to legal abilities when they evolve. Is there a way to make the mons keep the illegal ability when they evolve?

[Kaphotics]

No, because the ROM updates the abilities.

Change the ROM to stop changing abilities (nobody has done this before, so you're likely not going to either), or edit the ability in the save file editor after it evolves.

PKHeX is a save file editor. It cannot bypass game behaviors that update data.

[Meli]

Ah that's unfortunate. Thank you anyway