A trick could be to use FILE > MERGE command, this allows to import the OUTPUT SETS from one model to another.
I was able to use the "Merge" option and bring all the load combinations (as well as load cases and even the analysis set up,...) successfully, the problem is that the load combinations are not linked to the load cases,...?! I've tried to merge the load sets and analysis set as well but those didn't fix the issue. I also tried to Manage>Update the "Outset Set Menage" but that didn't help either,...
Tried renumbering ID numbers,... didn't fix it,... Tried different "Renumbering and Duplicates Strategy options" available in the Merge Menu,... didn't help!.
Tried to use the "Attache To Results" option available in the design tree,... didn't fix the issue,...!?
Please let me know if you have any comments.