So I played around with this some more... maybe I'm getting too comfortable with flashing or something!
I extracted the new PPST cab from the official Sprint ROM and stuck it on my PPCKitchen ROM (see sig), extracted, and ran it.
It took a long time, but finally said it was done with the update and rebooted my phone. I was expecting to see a PRI update to 2.04 as I did on the Sprint ROM... but this time my PRI stayed at 2.03 (which I upgraded a while ago from Bell's v1.33) and my PRL changed to 05075.
I wasn't expecting that, but everything on the phone is still working properly. I'll run some more tests to see what kind of trouble I've gotten into.