Yes, you can make cosmetic "fixes" but it would not be done properly. NoviBill is correct that the floor is an integral part of the entire camper structure. It cannot be taken up in a piecemeal fashion and repaired as in a home flooring structure. My local dealer, nor any dealer for that fact, has the equipment to properly fix the soft floor issue. Any soft floor issue, under warranty, is sent back to the factory and taken apart and the whole floor is removed and a new whole floor is put in. They have the equipment to do this and it is cheaper for them to do this, under warranty, than to, of course, replace the whole unit. To do this on your own, without the benefit of warranty, would require you paying for getting your unit to the factory, parts and labor for removing the old floor, cost of the new floor, plus other parts needed, labor for installing the new floor and putting the whole thing back together. Now it can be done this way properly as you say. A few thousand dollars later with a new floor and you still don't know the actual cause and maybe it was a water leak somewhere and then your back in the same boat. Not a job for a do it yourself-er.
Except........as I said above, there are other older discussions on this forum where people have welded bracing underneath the frame and or put down thin, (3/8 in if I remember correctly), laminate flooring to spread the walking load and found some success in their cases. You would have to judge for yourself if that would help in your situation. I will look for these older discussions and post when I find them to help you decide. I don't mean to run on but I wish I heard of this forum BEFORE I made my purchase as there is a treasure trove of sad/bad luck stories as well as great stories about the RV life.
GMC Sierra 2500HD Duramax
Rockwood Sig Ultra Lite 8315SS