a suggestion

It would be great to be able to instantly transpose a chord progression on the chord track especially a complex one that took a long time to put together only to realise that it was in too high a key?

Just select all the Chords on the Track. The Info Line will show the details of the first selected Chord. Change its value in Root Key (yeah iffy name) to what that Chord would be post transpose. This will modify all the selected Chords to change by that same amount.