I am NOT a lawyer, therefore what I say has no bearing in any legal court. However, according to MY interpretation of the GNU public license:
1) Any GNU software is able to be tinkered with by any tool at all, under its own license. "Preamble...'We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software."
2) Just because Kubuntu is a non commercial software, doesn't mean that you can't use it for a commercial purpose. the GNU license CLEARLY allows private software for commercial use. "Preamble....'Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.'"
Hope this helps,