Bib,
I'm not sure exactly what you're attempting but you may want to look at these articles.
https://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/23448/is-it-possible-to-make-a-child-scenario-alternative-into-a-base-scenario-alternative
https://communities.bentley.com/products/hydraulics___hydrology/f/haestad-hydraulics-and-hydrology-forum/199217/duplicate-parent-alternative-with-its-child-alternative-included/594256#594256
You can experiment by saving your model file, and trying the "merge" button (5th button) in alternative manager. If it doesn't do what you want, juts don't save the file or save it under a different name..