1. I've edited your subject line to remove the all-caps. Please read the EaseUp (←click) page on this subject.
2. Could you please re-state your question? I still have no idea what you want, or why you would want to load multiple versions of the same class. A bit of background would be useful. (ie, TellTheDetails (←click)).
Isn't it funny how there's always time and money enough to do it WRONG?
So if I understand your actual problem description, you have a class which behaves one way, and then after a while (I assume this has a precise definition) you want it to behave differently.
If that's the case, then having two versions of the class and having them both loaded by separate classloaders is, well, um, let me just say, it isn't the most obvious or straightforward way to achieve that. I would achieve that by providing the class with a flag which controls the decisions to work the "early" way and the "late" way, and then just set the flag when you want to switch over.