[Q] Can we hook class loaders?

Hello fellow devs!

I've got an idea for a module that involves reinstrumentation of classes at runtime and also preventing classes from being loaded too.
The problem is, I don't know where to start hooking. I don't really understand the way class loading works in Android.
I tried searching deep into the source code of the OS, found PathClassLoader, which resides in 'dalvik.system' package. I imagine it's not hookable...

So my question is:
Is what I'm trying to do even possible? Maybe I'm looking in the wrong place?

Also take note, modifying packages outside of memory is out of question here.