An idea for a screen that could be easily repainted was floating around in my mind. I threw together some plans and posted them a while back under the name "Proud Painter's Screen". The word proud indicating that the screen surface actually sticks out in front of the border. Here are those plans for anyone who might want to try to use them to make a screen.
This was designed to make a 98" 16:9 screen from a single sheet of white hardboard. With a little thought you should see that larger screens are possible with a seam that falls on the center piece. The two halves of hardboard would be securely glued to the plywood backing so that it should be possible to fill and paint over the seam without it showing in the image.
Here is another idea I had that might work to make an easily removable border. The two key items in this design are those self drilling plastic drywall anchors and the right size of finishing nail.
You need to select a size of finishing nail that slides snugly into the plastic anchors.
The idea is seat the nails in the border so that the point is just about to break through. One nail near each end and a couple along the length of the border piece. Then place the border piece against the wall where you want to install it. Now tap the nails in far enough to just hold the piece steady as you tap in each successive nail. Once all the nails have pierced the wall gently remove the border piece. Now install one of the plastic anchors where each nail hole is. You will also want to pound the nails the rest of the way into the border piece so that the heads are flush with the surface. You can now cover the border pieces with the black fabric or paint them flat black. The heads of the nails will be covered. If you are covering the border pieces with fabric be sure to leave enough space for the fabric where the border pieces come together at the corners.
The nails should now line up with the plastic anchors. You can simply push the border piece on with the nails snuggly slipping into the anchors. To get it off you should be able to gently pry the pieces up until you can get your fingers behind the piece and pull it off.
I'm sure other people must have had some ideas but have not posted them because they are untried. Well this is the thread to post untried ideas in. You may never have a use for it but it may help out someone else, and by posting it here it won't be forgotten.