For BUG it's pretty easy to pull down the full CustomAssets folder and use it as-is. Assuming you have BUG installed to the CustomAssets folder and nothing else, just swap in the new folder for the one on your HD. If you have it installed as a mod, swap the CustomAssets folder from SVN for BUG's Assets folder (renaming it to Assets of course).
BULL is a tougher nut to crack because you need to compile the C++ files into a CvGameCoreDLL.dll file using MS Visual C++. Others on the forums have done this, and there are instructions to get you going in the modders' forum.
Disappointment from Civ5, having my development machine bite the dust, and lack of time due to work have made getting back into BUG/BULL development harder. I do intend to do this at some point as I miss it a lot, but I cannot commit to any sort of time frame right now.
That being said, I believe Lemon Merchant is still working on a new BAT release, and she is more than fully capable of packing in all the new BUG/BULL goodness plus the cool stuff she's worked on herself. You'll have to look in the BAT threads to see the latest developments.