I am attempting to edit a Performance (A06) to change a Part Voice (#3) to a USR Voice and I Store the Performance. But that #3 Part's Voice will change to a different Voice when I jump between Arps 1-6. If I change Performances and come back, my new Voice is still assigned, but only until I switch Arps again. (moxF8)
This could be because you were unaware of what parameters settings are brought alone when you substituted a new Voice in an existing Performance, and which parameter settings were inherited from the previous Voice in that Part location.
This also can be because there is a parameter setting that links an Arp with a specific Voice. This is necessary because some Arpeggio Phrases only work with a specific type sound or mapping of those sounds.
There is a parameter called “Parameter with Voice” and there is a parameter called “Voice with Arp”
“Parameter with Voice” determine whether or not the (Arp) settings of the selected Voice are copied to the current Part when you change a Voice assigned to a Part.
“Voice with Arp” determines whether or not the Voice registered to each Arp is assigned to the edited Part. When set to “On” the appropriate Voice is automatically assigned to the Part in place of the currently assigned Voice. If the Voice is automatically changing when the Arp is recalled, then perhaps you want to ensure this parameter if set “Off”. (Reference Manual Page 83)
With the info you have given, the issue is caused/solved within these two parameter settings.