If OP is talking about backporting an update meant for 9.0, good luck with that. Only Opoisso and cyber2000 are pretty much the only two doing all the backports. So you'd have to be on their level of haxx0r skills to backport. They're hex editing etc.... and having to even do a lot of guess work in that so they take a long time. There's no simple autobackporter for 9.0.
I don't know for sure if it's based on digest, which I think is a checksum. I asked on discord, and I got no reply. I think all duxa repacker does is unpack the old patch, then makes a new one with the base, so you could do it manually. starting to think no body knows for sure.
I understand you, lots of games needs new patches, and I can name one which has lots of quality "The Outer Worlds", it has a 1.08 update minimum firmware required is 8.03, would like to have it full updated, because this game is well worth it