Originally Posted by KARFA

In terms of voluntary changes to rewards it is the case that they should only be done between destinations in the same band. Mexico and HK are different bands so that should not have been allowed really.

In terms of retaining the discount, again for any voluntary changes to these bookings you should have to pay the extra avios due for the normal rate. Again it might be you get away with this, but I would be concerned that the same happens to you as noted in this post when the ticket gets re-issued https://www.flyertalk.com/forum/32862663-post492.html