Looks like it’s extracting only the required eboot, sfo,sprx and prx files then making a patch file. Param.sfo will need additional edit for patch then moved out of image0 befor Gengp4 is used then brought back in after. Gengp4 also needs to be built for a patch and not app. Then build package.yeah ive seen and tested it ... fuck knows how hes done that its very fast!
Not sure about the update part though as I was never successful