Not to rain on your parade, but there are two relatively huge reasons why this isn't going to work.
Firstly, much like the ps1 classics, simply replacing data isn't going to work because it changes the eboot, thus breaking the encryption/signature.
You'll get yourself a big fat 80028F17.
Secondly, the PSP firmware used for emulation is a stripped down version with just enough there to handle minis, not full retail games.
You'll note you can buy full retail PSP games via the PS3 store, and while you CAN download them on to PS3, attempting to install them will only ask you to connect a registered PSP to move the game to.
These are two major problems that need to be overcome in order to get things going, and honestly, if you're struggling with a psar file i have significant doubts that you'll be able to patch the ps3 to allow booting of unsigned, unencrypted data.
~snip~
....once this hurdle is jumped the ps3 opens up to allow ps1 games to be run, and possibly pirated minis, but it's only one hurdle of many for psp emulation - i ca see psp homebrew designed for usermode (hen, etc), working, but retail games?, no, not without a hell of a lot of work.
Certainly not by replacing and messing with data in the current file systems anyway.