It is not so easy. Not only you need change NPDRM type, make LIC.DAT etc. etc. but also decrypting executable, looking there for direct paths to replace them and still some games could not works because some other checks are involved.
Disc images are the best and safe way which grants You 100% compatibility, blindly.
Besides that that, it is not job for CFW but for dedicated application, if on PS3 side, then i.e for backup manager like ManaGunz, multiMAN, IRISMAN etc.
Downloading packages from Sony servers outside PS3 isn't legal for many countries. I.e in EU it is like break-in to PSN, even if nothing is secured (imagine it like going to someone else house because door was open and taking something from there

).
Licenses aren't getting by installing PKG but by requesting SEN. Unpacking PKG on PC and PS3 have no difference.