UEM cannot edit the regsitry keys and values under HKCU/Software/Policies, since that location is protected and can only be edited by GPO or system management.
However since you use a USER GPO to limit the Office template, why not move that GPO to UEM and let UEM apply that GPO using the 'ADMX based settings'?
Use a condition on that ADMX based setting to only apply to the users that need the limitation and all other users can still use the office plugin.