You link variations to the program change numbers. Double-click on one of your variation names in the left pane and you ‘Assign a program change number’ to it.
In the menu bar ‘Options > Global Midi Settings’ there is a section about which devices GP will receive program change messages from. Ensure that is set to all devices, or that the Midi Mouse is one of the allowed ones.
This did work with the XR18 (Midi Setup page) toggled to USB Pass through, buy then my Midi Mate does not work. This is the same as when I use my Mackie MCU. I can use it or I can use my midi mate, but not both. So the work around for me, is to use a my Midi Mate connected to one of those cheap USB midi port cables, direct to my PC. That way I can use both.
Grateful for the help.
If you have an iPad, you can change rackspaces very easily. And wirelessly too. On my pc, I installed a free app called RTPMIDI. Then I connected both the iPad and the PC to the same wireless network. On the iPad, I run a lyrics program called OnSong. OnSong is able to sent a program change through RTPMidi to GP which will then change to the correct rackspace almost instantly.