In trio.xml, if you look at the bottom of the file, you'll find a list of the remote codes and the corresponding actions. I don't have the rio near me right now, but it seems that if you comment out (using <!-- before and --> after) the line corresponding to the power action, it would stop that action. Also, there are 2 sections, one for the remote and another one the front panel. Just make sure you comment the right one.

Don't forget to stop and restart trio to test.