Which classes are unmodifiable and cannot be intrumented and is there a way to bypass it?

Which classes are unmodifiable and cannot be intrumented and is there a
way to bypass it?

When trying to instrument classes such as java.util.ArrayList, I was
getting java.lang.instrument.UnmodifiableClassException.
you can check if a class is modifiable using
Instrumentation.isModifiableClass().
My question is:
Which classes are not modifable? How is it determined.
Is there a way to bypass this?
By the way, I didn't get this exception when working with HotSpot or
Jrocking, only with IBM JVM.
Thanks, Gilad