If you do this on a regular basis, it would benefit you to make a Motion template and publish it to the effects browser in FCPX.
However, all you need to do is add the unmodified compound clip to the timeline, then select it in the timeline. Go the Clip menu > Reference New Parent Clip. This makes an independent copy of the compound clip. That is, any changes you make to the this new compound clip do not affect the original compound clip in the event browser or any other project.