You can't learn to the Power button on the RCA, so just put on/off on a different button. Any other button will accept a learn (except the device buttons).

You can learn to a shifted button (Setup = Shift). For example, if you press Setup prior to learning or using any button, it keeps it's original function but does the new function when you press Setup first. So you could keep LiveTV's original function, for example, and learn on/off to Shift-LiveTV. Then pressing Setup LiveTV will turn your device on/off. Using shift effectively doubles the number of buttons on the remote.

More about shifted functions here:
[Link: hifi-remote.com]

And if you'd rather do all of this programming from a computer, check this out:
[Link: hifi-remote.com]