Any kind of patch you made and believe is good enough to go in officially can be posted here for the devs to look at and apply if they believe it's the case. Since the game runs off SVN it's usually recommended that changes are made over the SVN version and posted as .patch files which can be generated with your SVN client (I use Tortoise SVN which works very well). Anything that helps with the game is useful... code changes, textures / models, sounds, even maps. So if you made anything interesting just upload the patch onto a file hosting website and post the link here with a description about the change if you wish.
To start off, this is my first code patch for Nexuiz (discussed it in #nexuiz.editing on irc tonight). This is a feature I wanted to see in the menus and since I wanted to give my first shot at making a code patch for the game I made a change which includes all weapons in the Mutators window to be played as arena. Currently in SVN there's only the Rocket Launcher and the MinistaGib / NixNex in that category. My patch makes the arena list complete and adds all the weapons to it so whoever makes a server can easily select any weapon to play with... most useful especially when someone wants to train theirselves with a certain weapon to gain a better skill with it

The patch can be downloaded from this link and a preview screenshot of the list over here.