How can I change elements of the selected L&F ?

I've very little experience with manipulating L&F or UI elements in general, so bear
with me if this is not the right question to ask.

I really like combinations of the way elements look in a couple of IDEA's L&F and
would like to be able to have some elements from a particular L&F rendered that
way in another L&F. For example, the Alloy Glass theme is nice for it's colours
but the Tree view expansion boxes are so odd in comparison; can I have the other
Alloy themes' tree view expansion boxes instead?


Cheers,

Bonny