If I understand your question and objective, then I’ve done as you describe. I used to have an Eberlestock frame and would simply lash a pack to the frame for carry. Equally, my new 10 day pack is a Mystery Ranch 6500, I installed a Mystery Ranch Load Sling on the frame and use both simultaneously. This lets me drop the pack for load hauling, but still have the Load Sling handy. It also lets me stow a rifle or bow on the back of the pack very conveniently, supported by the Load Sling like a bucket.