Hi Emmanuel,
The
Main Menu>Character>Mirror Tool and the
Main Menu>Manager>VAMP…
are the closest I would suggest.
http://www.cineversity.com/vidplaytut/character_rigging_in_r12_mirroring
However, I’m not certain if that will completely give you what you want, as it duplicates and not necessarily overwrites information.
I’m uncertain as you write you want to copy it to one half, but then write the other half is already complete. Complete in modeling I assume. I’m not certain if I follow here completely. Why not deleting the half and go with a complete symmetry? If there is something different, then it might be a good idea to check the differences before you copy something over it. Again, not sure I can follow here the idea.
Perhaps you copy the Pose Morph “Pose” and then flip it (right mouse click, RMC)—connect via XPresso (set driver/set driven) or both to 100% and RMC
>To Mesh, then drag the new mesh into the Pose Morph list as relative.
All the best