In a multi-solid part. You can "Make Part" from a selected solid to create a new part, but this part is linked to the original file meaning any modifications (on a feature which was done in the original file) needs to be done in the original file.
What I would like is to create a "Make Unlinked Part" which makes a new file of the solid but contains the features used to make the part. This would be it's own separate instance. Any dimensions which used another solid to work out it's geometry could just pop up with a "re-dimension" message of sorts.