Can Raise/Can't Raise

Is there a way to change units type from Can Raise to Can't Raise with triggers?

chaos?

Chaos would be the only way. Nothing else permits that field to be altered in code.

hydra ability (summon unit on death) remove corpse, create other unit.

That's not really changing the unit, though, but it's an okay workaround. I guess you could always CreateCorpse() for a unit without a corpse normally if you really wanted to.