Update on how it went: I was running the 2.2 update from over a week ago, and rooted using EasyRoot. Had SetCPU running, and a couple other small apps for root-only users just because, but no ROMs or backups. I went ahead and updated Jrummy's file from Page 6, and the install went without a hitch. Had to re-root, reboot, then restart SetCPU.
The only issue I ran into was a couple of large apps I had moved to the SD card to save internal memory; their icons disappeared from the list of apps, and the on-screen icons changed to generic Droid icons of some sort, but they ran just fine. I re-installed them using "App Monster", a useful tool from the Market, and they reappeared in the app list. I deleted the generic icons and replaced with the new ones, and all is good again.
Seems someone else had a similar issue; it makes sense because I had a previous setup referencing files on a separate drive, then did a rewrite, so some of the references didn't get copied. No big deal, and no other problems.
Thanks everyone for your help; I'll be digging through other forums as I get deeper into this, as I get braver. :icon_eek: