The USDM STI is not supported, yet. Once we can read and flash, we need to start mapping out the ROM file. So it'll be awhile. I suspect fuel and timing maps will be easy to spot, but some of the smaller stuff will be tough to find.
You can (and I would suggest) backup whatever is on your ecu as a first step.
I wouldn't call things too solidified yet. None of it is terribly user friendly, but its coming together. There are a handful of 2002-2005 WRXs and some JDM STIs that are supposedly working.