Hacking / modifying your drone and other DIY stuff. What are the possibilities?

I'm currently in the market for a drone - probably something fit for a beginner. I am curious about the possibilities I have with one. I love to modify my cameras, make custom parts for them, and do all sorts of DIY projects with them. I recently opened up a Nikon D40 to remove the IR filter to convert it to a camera that can capture Infrared as well as visible light. I've also made custom rain covers, lens filters, and have loaded my DSLRs with modified firmware so as to increase the video length and bitrate, reduce noise for better star trail shots, and other things that basically access what the cameras can do but were otherwise disabled by the manufacturer for whatever reason.

I was wondering if there is an equivalent of all of that with drones. Do people build their own propellers or landing gear? Waterproof their drones? Can you "overclock" them or modify their software to give them an extra boost? Custom paint jobs?