Chipper,

Try reading the whole thread. The power off is in rcvr_0842 as efc 170. As Rob said, it's available as an upgrade if you have an upgradeable remote. Whether ueic will still upgrade the discontinued P-8's is something you'll have to ask ueic. The OTHER option is to use JP-1 and make the upgrade yourself. OR, do as you said, learn the off command and take your chances with it in macros.
IF ueic won't upload the upgrade, and you don't want to mess with the learn, then I think you would have to decide whether to do the JP-1 route, or get a newer remote, perhaps the 8910 or 9910 which can be upgraded via the modem upgrade feature they have over the phone or thru a downloaded .wav file. Or get a newer remote and JP-1 it.
Jim