anyone know how to make a decal change from one into another?

I'm doing a recreation of Disney's Haunted Mansion, and one of the scenes in it is the changing portraits after the stretching room. The pictures are normal, but when lightning happens outside of the windows infront, they change into a ghostly version of themselves until the lightning stops. Does anyone know how to make a decal script that can change it from one decal to another like taht? All the other ones i've tried using don't work, the decals just do not appear