I don't know about a mod, but if you just want to leave some stuff behind never to return to it later then you could just dump it out of the airlock (or deconstruct / sell) before switching.

problem, what if my hoarder instinct says to keep everything cause you never know when you might need it?

I've never gone back to an old sub, have you? If you leave some items on the old sub, what are the chances that you'll want to switch back to it?

I just sailed through to the end of the main campaign in a Dugong (or my custom variant, anyway), I had a few extra crates of materials and such and didn't need most of the stuff in them, in the end it felt a bit trivial defeating the final stages because I'd already been there and knew what to expect, so was prepared. Only experience will tell you what you actually need to keep and in what quantities.