it really depends on what you do with the rom really.
ppf can do the job for smaller things, but i do recommend switching over to xdelta for checksum validation with psp isos.
it's just a bit more comfortable that way.
alternatively, you could just always extract the iso and patch the internals instead, although the biggest issue of this is
that currently there are no good tools to put a psp iso back together through commandline or so, and having users deal with
umdgen is not really convenient. That's the main reason i set out to just get my own isobuilder done for whatever i need to patch.
the other thing with patching internals is that if you patch the elf file, you will have to decrypt it first, othervise your patch will just
always contain the whole damn elf in the patch, which is also not really convenient, not to mention the copyright aspect of distribuing such things.
fortunately deceboot ( http://www.romhacking.net/utilities/1225/
) solves that issue.