I thought people knew but guess not.
You can unpack with maths ps3 psp pkg extractor. google it to find link for download, I could only find one that links from another site. Or use PSDev, http://www.mediafire.com/?5kpbnpb4bujs3rz
, tools to extract pkg.
Then repack with Hackerchannel ps3py will create a pkg that will install on 4.11 (as i haven't upgrade so 4.20 haven't tried)
links for PS3PY make_pkg
or for Mac OsX
I tested with earthworm Jim and it installs on 4.11.
using psn_npdrm_package is a waste of time in downgrading to install a pkg!!!
So extract .pkg and find EBOOT.BIN preform readself on it and find contentid, copy and paste that into the make_pkg program. it will take a moment to build the pkg so be patient.