Hi,
Yes, it can be done if you proceed like I said.
The point is to create (mirror) the left handed part with all features of the original part, with new from procedure, but you will not have any link between left and right handed CATPart.
If you want to have a link between these CATParts, you need to copy-paste as result with link all features, mirror and then add new features to the mirrored CATPart.
Regards
Fernando