It is not a big risk really. Thanks to jadburner who was kind enough to dump the firmware from his drive, I've now got a copy of the PT11 firmware, so now that a firmware dump exists, it is easy to go back to the original firmware should you want to do so. Crossflashing to iHBS112 doesn't require any EEPROM adjustment, so it is as easy as flashing the drive with an iHBS112 PL0x firmware using the unlocked flasher method.
Incidentally the PT11, dated 2012/12/05, is newer than the other existing iHBS112 (and Plextor clones) firmwares by about 2-3 months. Here's a copy of the firmware in case someone wants/needs it: http://www65.zippyshare.com/v/73395471/file.html