One good thing about many games built on Valve's Source engine is that developers often release the SDK (software development kit) for them. And so it is with Zeno Clash.
Developers ACE Team have released the tools - which will allow users to mess around with items, characters and environments within the game - along with some paperwork on how to get the most out of them, on their wiki page. If anyone feels like giving the guns a little more heft, I'd be grateful.
SDK files & documentation [ACE Team, via Shacknews]