Well, it worked just fine - but oddly enough brought me back to PRL 60652 (I had 60654) - so off to update again, either OTA or manually, and then who knows if it'll all be worth it.
Got the new one OTA by using the Updater. OK, what next...
Update: this was definitely worthwhile. FieldTrial shows I got a boost of a few db, and I need every point where I live.
One question: should the PPST file be deleted and/or the cab uninstalled once it's done? I think the cab put itself in the Remove Programs list as just "Customization Tools."