To force them into their true shape? It can be done with magic, just as there are spells of true-seeing that allow one to see through such transformations.

Personally, I would be more concerned with detecting such shapechangers rather than returning them to their true shapes. My understanding of such magic is that he might be weaker in an animal's body, or at least less able. I doubt one would wish to fight in the body of a goat, or a rat, or a raven.