You used to be able to swap partial sets (just cloths, just jewelry, just weapons) by having all slots that you don't want changed empty when you save (ie. take off weapons to save just armor and jewelry). Then when you load that saved set, your current weapons would stay and only the new armor would be swapped.
In one of your recent updates this changed, now, one of my weapons (not both) get removed when I load a set saved in the manor described above.
This was intentional. A future update will allow you to intentionally ignore slots when saving. More people wanted it this way by default, includinf myself.