oh my god.
That's way worse than I was expecting to see....wow.
First of all I can't believe you're not allowed to paint! This room is in serious need of some quality paint! It would be the best solution, honestly....but they said no, so let's think here...
I'm afraid all the solutions that I am thinking of might be a little expensive, but I'll put them out there anyway.
I used to work at Macy's in the visual merchandising department, and we used this technique all the time. To recreate the look/color of a space without actually painting, we used foam core board. We would get large sheets of foam core (4 foot by 8 foot), and tack them to the wall with bank pins (the largest pin pictured here, without the T shape on the top:
http://www.aaimporting.net/Everyday/pins_wire.html). We would hammer them in on an angle until they bit into the wall, and then use wire cutters to snip off the rest of the exposed pin. We would start by tacking along the top, and then down each side, then butt the next piece and tack it, etc etc. If we were covering glass or mirrored surfaces, we used double stick tape.
Often we used fabric to cover pieces of foam core for particular themes, and we would lay the fabric down on the floor, set the foam core on top, then gently staple gun the fabric to the back of the board, keeping the front smooth. We would lightly steam it if it was badly wrinkled. Foam core is expensive, but if you run across something similar to use this method, like huge sheets of thick cardboard, it might work. It might work on the smaller wall under the windows too. If you do use foam core, make sure to use a NEW sharp blade in your utility knife and a straight edge to cut it, otherwise the paper on top will look ragged and little bits of foam will flake everywhere. You will need to cut out little windows in the foam core so you don't cover up any electrical outlets or light switches. And if you are cutting your foam core, don't walk, stand or kneel on the board, it will dent.
The other solution would be to "wallpaper" using something that is not permanent. For example, staple gun some long pieces of burlap or felt to the wall, or even cheaper, maybe try a roll of gift wrap, or newsprint. If you go to a local newspaper printers, sometimes they have left over rolls of plain newsprint that is too small for them to use, but is a TON for you to use, and they might give it to you for free or for very little.
Lots of large posters might help too. You could even make wallpaper: tape together smaller pieces like posters or magazine pages into a large panel, and then staple gun that to the wall so it's a big sheet, and not using a hundred staples and making a ton of holes in the wall. You could also use fabric, king size bed sheets would probably work well, and basically make looooong curtains.
Separating the space into bedroom and study area might not be too hard if you have some kind of furniture that can be a divider. If you have a bookcase or couch, you could put it in the middle of the room to split the space, or use something like a large floor plant or folding screen to help too. Honestly, I would probably not worry about dividing the space, and put any large pieces of furniture against the craziest part of the walls to hide the most of it that you can!
Good luck! i would love to hear what solution you come up with.
