Well, logically thinking, you could always place your swapped out limbs back on right before you leave the dungeon, then apply healing to them immediatly once you are out of the dungeon, as they would be damaged still. And since you can store them inside of your inventory too, they won't be too bad off since time doesn't move inside of it.
With this plan, you ready yourself and prepare the parts first. Her left arm and wings for certain you will add. The question is how do you attach the wings though? They are poking out from her hips instead of her shoulder blades, and honestly you are unsure as to what or where you would have to cut in order to remove them properly. This leaves you with but 1 option. Taking her entire waist.
Using your new fingernails, you cleanly remove her legs, and upper body. You prepair yourself, and first remove your legs, then waist, you quickly slip her waist underneath your torso, and then reattach your legs. It took you maybe 10 seconds, but it hurt like a bitch. Once everything was healed back together, you swapped your left arm for hers too.
There are 2 other parts which were of significance. Her ears, and her voice. Unfortunately with beheading her, you cut her vocal cords. But her ears are still good. She has way better hearing than you, and made your initial sneak attack meaningless with them, thus causing your struggle with fighting her in the first place.
Two pairs of quick snips later, and you are now the owner of a pair of pointed ears. And it is as you suspected. You can hear far better now. The difference is crazy actually.
Well with this all said and over with, you gather up your detached parts and store them. You also take the rest of her body, just in case. It is a bit weird seeing unfamiliar and very feminine arms with flawless, fair skin and long incredibly sharp nails moving at your will. The skin does not match at all, and there are visible seams where your original skin meets up with her skin.
Your armor is in a pretty bad shape now as well, with numerous new holes cut into it in order to fit your new wings, tail, ears and breasts. Also, since your ass now is bigger, the bottom half of your armor had to be cut loose, and now hangs over your ass kind of like when a woman wears a skirt that is a little bit too short to cover it all, and a bit of her ass cheeks are left completely visible.
Of course your front matches the back too, and is just loosly hanging armor. Because of this, you chose not to return your manhood, simply because your loose hanging armor would end up smacking it far too often to be worth doing it. You also are wearing her panties, since they actually are a piece of magical armor, which is quite a rare find and even has a movement speed upgrade stat, and at least can cover you up if not by just a small a bit more.
You spend the next 2 hours still inside the boss room, moving around, jumping, and practicing using your nails instead of your sword, as their lengths made gripping onto it so difficult to do that it made any kind of halfway decent attack a crap shoot between landing a weak hit, or just throwing the sword outright as it slipped out of your very loose grasp. Needless to say, your damage output went up tremendously, but your combat style now had to be changed significantly as well. You also have to be more careful now too, as your arms no longer have your full armor on them besides some makeshift leather wraps. Granted that they have a much higher defense anyways. Boss monsters are not to be overlooked after all.
Finally, you did try out flying. You quickly learn that wearing your heavy armor makes it almost impossible to maintain flight, thus explains why she was wearing almost no metal on her armor, and instead was covered in magically enchanted underwear armor instead. But while you can't fly continuously like she could, flapping them does still move you faster, your falls are also slower, your jumps are higher, and you can even glide a bit.
They also are a great defensive option too, as they are quite strong. She blocked your sword swings quite a bit with them durring your fight, and had taken absolutely no damage to them at all. If it were not for you catching her off guard when she came in close so that she could deliver the final blow to you while also mocking you, you would never have won that fight.
Now that you have gotten your balance again, though it still is a bit wobbly at times thanks to your two new heavy weights hanging proudly off of your chest, you feel it finally is time to go down to floor 4. Making sure everything has been collected, you head for the exit and take the stairs down.