For the sake of this guide, we are focusing on the accessible ones above. Of course, any package on the “np” (the retail) environment is encrypted with the retail package keys – short of an internal box, any TEST/TOOL over 1.60 will not be able to decrypt these. You could get the packages, downgrade, install, and upgrade again if needed, but it is of course, a pain to do.
There are however the sp-int and prod-qa environments which tend to have (for a short time) packages that a debug unit can decrypt. The biggest problem, is that they tend to only be available for a short time.
You can check (redacted by me) to see if there is a package available - if not, and you happen to come across one, please add it in for the rest of the community!
So the trick becomes: Do you get a nice debug patch quickly which you can then decrypt, and re-use the SELF(s) to burn to disc, or boot from HDD. Or do you get a retail package, downgrade, become limited to where you can run it from – best bet is to find the debug package!