Once you have Partisan/Conqueror, is it worth giving up expertise on two armorings in order to pick up the 2-set PvE bonus (+15% crit to Tracer Missile/Grav Round). I can not live without that set bonus, especially given the reduced effectiveness of crit rating.
Better to replace them entirely with PVE pieces instead of armorings. New bolster does NOT like it when you mix and match mods with expertise and mods without expertise. For example: Using a PVE weapon and putting in an expertise weapon will actually cause you to lose expertise.
My guess is a completely PVE piece will have more bolstered expertise than a mixed piece. I'd probably go with dread guard for best results if you just HAVE to have that set bonus.
On the other hand, the overall loss may not be worth it anymore at all period.