I believe the way it works is that the receiver builds a lookup table of the available transponders you can see and their content based on the DVB headers, and when you tune to a channel it consults that table. So in short, if you can't see 61.5 but can see 77, and a channel is available on 77, it will automatically go there.
If you can see both, I believe it has a priority list. I don't know which between 61.5 and 77 is higher in priority. My guess would be that a CONUS beam is higher priority than a spot beam though, because a particular viewer could be in solid CONUS but on the very edge of a spot.