Actually pfhorslayer has already made an unpacker! I asked him and he was kind enough to upload it for me. He has an os x binary, or the source code which could be easily compiled. Right now it unpacks the map (so you have a file just like you would have in your cache), and it generates text listing all of the items in the index. He has identified several of the tags, but there are still plenty of unknowns. It's pretty cool.
I found that I could successfully replace ui.map with a decompressed ui.map, but could not do the same for bloodgulch, but I have just been putting the files in my Y folder anyways, so it doesn't really matter.
I have tried changing the filename paths, but that doesn't seem to do anything. I completely changed a bunch of file names in bloodgulch and nothing changed. However, I did change the title 1 track in ui.map and it stopped the music at the main screen. This is the only time changing the filename has done anything.
Are cache000 and cache001 the files that actually contain all the files, and cache002-005 are just for indexing?