It's a bit more complicated than that.
1. Some of the code in the PSP version is totally different (like the graphical system, but also file loading and stuff like that)
2. Some of the code has been altered, to implement the new items, jobs...
3. Ignoring the two precedent points, you would still only be able to relocate very simple hacks. Any ASM that need to add code will be complicated to relocate automagically.
4. Even if you could do all that, it's still a different game. The old ASM hacks could (and will) cause issues, for example, bad interactions with the new items (because of uint8s)/the new jobs, the spritesheet issue, etc etc.
You would definitely succeed with simple asm hacks, but for the simple ones, it may be easier to just port them by hand. For the most complex ones, you would want to port them by hand anyway to make sure they're correct.
However, you're right about one thing: it is viable to grep for matching binary sequences to find some offsets. That would help you find some matching offsets before exploring the differences and patching by hand, essentially leveraging the PSX documentation.