Adding format="#\." to the child elements "TrackNo" or "#" does exactly that (inserts a dot after the track number).
Unfortunately, that won't work in your case. If I'm not mistaken, this attribute only works when the track listing is set to "NowPlayingList".
It doesn't seem to work with "AlbumTracks", which is what I believe Rdio Style is using.
So either change line 18's element type to NowPlayingList or make a request for AlbumTracks to also make use of format="#\."