[quote=@TinyKiwi]
If I were to do something very specific with magic, namely having a character with a prosthetic limb made of enchanted stone, would there be anything to prevent that?

[/quote]

Nothing would prevent that, considering how it's just controlling magic rocks. The quick rule of thumb is that you can't use magic to harm someone without creating or using a medium to do so. For example, you can't pop someone's head like a grape using the classic head explosion spell, but you can create a concussive beam that'll do the same thing if it hits.