1 - An expression of bad blood/beef through music or poetry. The intended response is that the issue will not spill over to people who have no knowledge in the subject. Or, moreover, keep the issue silent from unrelated parties.
2 - An old gang term thought to have a similar meaning. Instead of resorting to violence the parties involved, respectively, try to resolve the issue peacefully. Presumably also through a form of music or poetry.
It refers to something that will most likely change. Something written in stone is permanent, whereas, wax can be melted down and appear as being brand new.
Zachary: Keep it on Wax, brother.