NONONONO!!!
AND AGAIN NO!
Don't touch shaders coming from Xonotic/Nexuiz, because if you start distributing pk3 with these shaders, that have the same names as the original ones, it'll cause problems for all those who download it.
If you create your own shaders, feel free to use default ones as examples, but don't overwrite/modify them.
Also, for properly naming and placing your textures/shaders, here's a guideline that I strongly suggest you to follow:
http://forums.xonotic.org/showthread.php?tid=754
Also, there was a problem that was discovered lately, that the 0.1 version had some odd jpg version, that the engine could handle, but not radiant.
"One should strive to achieve; not sit in bitter regret."