I've done this a few times in blender, just load up the obj, making sure you select to keep vert order, then in the UV editor workspace make your adjustments and export the amended obj, again making sure you keep vert order, then simply replace the original obj with your new one and load. After EZCloth I was going to write EZUV to allow you to load different UV maps on the fly (obviously if the objs were the same in terms of verts) but I never actualy got around to it, I think because you couldn't add tverts using python but I really can't recall the exact details.