The sacrifice spell..?

Hello friends,

I was wondering if you can change the sacrifice spell? like if i want an wisp to become.. let's say an archer by going in into a building. Can i do this somehow? i have looked into the spell but i can't change the "unit type" it will always be shade. If you can can change this somehow, can sombody help me with this?

Thank you very much for your time :D

You could do that but it would be using a dummy spell and triggers, not with that ability.