>>19750389To be honest, it probably wouldn't be THAT bad.
We know the horn is vital to the pre-evolutions, particularly with emotion-detection, but Gardevoir's entries read nothing about the horn, so it's likely lost some importance, becoming more like an appendix at this point.
The horn is likely made out of some sort of Keratin or other material that is meant to be on the exterior of a life form, with a fleshy center, much like an animal's claws or more similarly, a Rhino's or Ram's horns..
You could probably remove it, ableit probably at sizable risk, as long as you absolutely ensured that you stopped bleeding in the large area that would be left open and closed everything up in a proper Operating Room. The only seeming loss is the recovery time and a large scar.
You'd probably ruin a Kirlia or Ralts though.
Game Freak really should add Gender Differences to the Ralts line.
Have this neat Pokefusion.