http://forum.coppermine-gallery.net/index.php?topic=3185.0 :-\\
Any mod is going to have to be thoughtfully moved over to 1.4, I would hazzard a guess that no mod can be moved without changes.
I would aslo further suggest, that many mods, can be re-written as plugins, and therefore your install can remain code compatable with Coppermine; upgrades (and security updates) can be MUCH MUCH easier.
There isn't a lot of detailed information available to developers however there are some examples available. Check out cpg-contrib.org's forums for a few plugin projects and discussion boards that are for DEVELOPERS creating plugins.