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2.5. Policy on hacking another people's code.
If you're going to do little clean fixes, go for it. But if you plan to do changes to some API or rewriting some code please ask / tell the author. Modules on CVS have different levels of maturity: some of them are being developed actively, other are very stable and changes to it should usually go first through the module maintainer. To help clarify this situation, usually, there is a file called README.CVS included on every module on CVS where the policy is detailed for the hacking you can do to a module.
If in doubt, ask the gnome-hackers@nuclecu.unam.mx for assistance.