Word Press Theme

With word press, you have this concept of themes that can literally do anything with the underlying platform. There's almost no limitation to what i can do - a theme is not just about c, s, s and h t,. It's also whatever p, h, po, more or less, that i want to add into the system. And obviously, when, when i do something like that, how can you control what i do? What process can you put in place to insure that somebody doesn't install a theme, or maybe even just a plugging?