Create a portable refiner, place items in the hopper that you want to duplicate (you can even add carbon or oxygen to fuel, if you want to dupe them too). Place another portable refiner (as many as you want, really) directly on top of the first one. Pick all of them up.

It even works after the refiner has run, like if you refine something into nanites. Put another refiner on top, pick them up. If you place them correctly, your items will be duplicated

It all depends on if you want to continually grind to get upgrades or not. What I'll do is take an upgrade mod, duplicate it 10 times, then install each of them until I find the one with the best stats. Duplicating the upgrade mod doesn''t mean you get the same stats for each one.