Lots of posts on this topic - but I did not see anything that answers my question... Hopefully you can.
I am on 2015. I created a mirrored part in an assy as an opposite hand version.
(what does "isolate selected component" do?)
I got my part and I am happy, but I needed to make a change in the original part. The change is not reflected in my mirrored part. So, I edit the MirrorComponent feature and look through the selections and my preview shows the change I made. I happily click "ok" or "done" and the change doesn't stick - the left hand part reverts to before the change. I tried all kinds of things - the result is always the same; the preview looks great, but the model is old and unchanged.