Do you have a Copyright on LMMS? Everyone who is wanting to make
simple cosmetic changes an claim a new product are committing
copyright infringement I believe.
Paul, if you read the General Public License, it makes a point to mention the legalities of selling the software. Companies like Novell and RedHat currently use this to sell a GPL product by charging for their versions of Linux.
It is perfectly legal for Aaron to repackage and sell LMMS so as long as code changes are republished (which would be in his best interest anyways). His artwork can be separately licensed under what he chooses (unless he borrows that too, then he'll be responsible for abiding to that license too).
What is more viral to a community is a license that does not have strict requirements of code "kick-backs" (Like BSD, MIT, Apache).
Apple chose FreeBSD for they're OS X operating system. The BSD license allows them to close the source and contribute what they want to the FreeBSD project. The GPL license does not allow this.