I want to morph a hero into another and then repeat it with new heros, like morphing a paladin hero into arthas and then arthas into a death knight hero using metamorphosis. the problem im having is that when i do this the hero doesn't get the new metamorphosis ability and just continually upgrades his current one. Its sort of like a evolution but involves about 8 heros each.

Can this be done with items so that i don't have to worry about room for attack spells or can it be done with triggers or like a spell book?

Are you perhaps searching for some way to simply swap the models? Would that be a simpler solution?

I'm pretty sure it can be done easily with a Trigger or two. Just make a dummy spell the event, and make so the trigger will only activate on the condition that the person using the dummy spell is the one you want, and make the trigger a simple unit change. It should be there...

Thanks