Because of what we discussed above, the PLG boards will either share a MIDI channel with an internal PART or you can replace the internal PART with the PLG Voice. Setting its MIDI channel of OFF and then storing the data can deactivate a Part, whether it is internal or PLG. However, if you are in a situation where you are using the MIDI jack and you just want to stop the PLG board from layering, here is a short cut to bypass the board completely:
-Press ULTILITY
-PAGE [>] right until you reach the PLG1SYS screen
-Set the PORT to 2

This works because the internal sounds of the Motif-Rack default to PORT 1 and by setting the PLG board to PORT 2 you have effectively defeated it from receiving data via the MIDI IN.