for a non China way to flash the file, use OBDxpro, it's 150 and open source with good support over on pcm hacking...
you might find some help for a file there but as for us mortals, gm doesn't give you any way to save the file from their site. it's all done within their locked software you have to use which runs inside a Java setup, nothing is saved to your computer and when you're done there's nothing useful let behind.
as I understand it, best way to go about what you're trying to do is buy a bcm, open it up. find out the manufacturer of the chip and use their software to access the data on it, not involving gm at all. chip sets are like Lego they are made generic with a huge manual and base software, it's then up to the buyer to hire software engineers to write the code for what's needed for the unit to do what they need.
I could be wrong on all that, but that's how I understand it. it took years for the diy guys years to get into the first obd2 ecm's.