But the "Mirror assembly" does not add the constrains,just the part. So you have to constrain the part anyway. In this case I would use "move with copy" and than fix it on the place. Seems as quicker way to me .
Is it the same part or a mirrored (symetrically opposite ) part?
Sometimes they are the same thing, other times not.
If its the same part number, I'd reposition and constrain it. If its a sym-opp part. makes a kinked mirrored body then position and constrain it.
Elmhirst Industries, Specializing in Prototype sheet metal stampings and assemblies
Production: NX 12.0.2 / Autoform r7 /WorkNC 2018 r2
PC: Rave Cadbeast: Intel(R) i7-4790K CPU @ 4.GHz /32gb ram /NVIDIA Quadro P2000 on Win10 Pro