The following does not apply to Humax Youview boxes but does apply to almost all other Humax boxes released in the past few years, including the Foxsat-HDR and the HDR-FOX T2.
The solution to your issue was original posted on the now defunct hummy.org forum:
1. Switch on your TV set and the Humax product that you wish to change the remote code.
2. Make sure that the other Humax product that you do not wish to control is in Standby or powered OFF at the mains.
3. Point the remote control towards the remote control sensor of the target receiver.
4. Press and hold the 0 and OK buttons simultaneously for 5 seconds until the PVR button on the remote stays red.
5. A message will appear on the TV screen:
"You can change the remote control mode.
Press a Numeric Key ( ~ ) to select the mode
Current mode: Mode 1."
6. Press a NUMERIC button (from 1 to 6) to select a different mode.
7. A message confirming the change of Mode will appear on screen.
Neil S, March 2014