On Astra many transponders contain references to other transponders, so
if you have one initial transponder chances are VDR will find other
transponders, too. On Hotbird it looks like they don't have these
references, so you need to define at least one channel for any given
transponder to make VDR automatically find all the other channels on
that transponder.
Later VDR will automatically scan the TP frequencies, but that's not
a priority at the moment.
I may be wrong, but whilst the contents of each transponder may change
frequently, it is rare for the basic parameters (frequency, polarity and
symbol rate) to change.