This must have been a SolidWorks 2014 thing because SolidWorks did not used to do this when we were on 2013.

I am wanting to mirror and assembly, and only 1 of the parts needs to be an opposite hand version, while all others can remain unchanged.

The problem I am encountaring now is that the mirrored assembly and the opposite hand version part permanently inherit the custom properties of its parent!  I cannot change, edit, or delete the inherited custom properties!

This is an example assembly.

The part highlighted in pink is the one I am creating an opposite hand version

Notice how Custom Properties is NOT one of the options under Import Features menu so I don't know if its checked or unchecked? I'm guessing its checked by default?

In 2013 when I used to mirror assemblies like this Custom Properties was one of the options to check/uncheck under Import Features menu

So this is what I get for both the assembly and the opposite hand version part.  fromparent+ for all the custom properties.

and this shows how they're not changeable

I cant erase them, I cant edit them... see how they're greyed out?

This is a real problem because these custom properties show up in our BOM, and the assemblies and parts that need to say RH still say LH and we cannot change them!

This was not a problem before.  I used to mirror assemblies and parts like this all the time and the mirrored parts/assemblies would have nothing in their custom properties and we manually typed in new properties for them.  The only thing I can think of that changed is that we upgraded to SW 2014.