In the settings of the Kobo Glo, one of them says "Beta Features" which has, Chess, Sketch Pad, Sukoku, Web Browser, Unblock It, and Word Scramble. My question is, can you add any more "Beta Features" to the device? Would it be possible to program them yourself?
I think that you need to do some advanced hacking, there is no official way to add more features to the default firmwares AFAIK.
Anyway it is possible to apply external patches and customized versions of the firmware; it is not something that I have done myself, but at MobileReads they have a complete section dedicated to Kobo devices' hacking.
In particular, you might want to start from the thread named "List of Tweaks / Hacks / Mods" that is an index of everything is being posted on the forum. There are many different new features/hacks/patches, each one of them has its own way to be added, so I fear that there is not a generic way to perform these modifications. You should look specifically for what you want to change and follow the instructions for that particular hack.