how to change the skill "possess"

I think it would be a Fun Thing to have Phoenix Downs be Useless, and instead, upon Character Death, have them swap places with a Fight-less Ghost Character, and only a Successful "Possess" would revive the Character.

This would be possible I think. It's similar to morph, the only difference is that the character would be invincible. The other thing is to modify Possess in order to revive the character.