Can I paint a rough wall with chromakey paint to make a green screen?
It depends on some factors.


For example, how far is the wall from the main actors? If you have some good spacing, the texture can probably blur out due to DOF. But as on a green screen you need to maximize the focusing range, probably you will still have some texture visible.
How even is the light? You can probably lit good enough from both sides to eliminate the shadows on the texture produced by the other light.


In reality, you need to test. You do not need to paint in green before making these tests. Use your wall as it is, and use that color as a chroma key, you can even use white. Put a subject with clothing that has no white (or whatever current color you have now) and make a test. If it passes, it will probably work better when painted in green.

If you do not need a large green screen, you could probably use a frame made of PVC and green fabric.

But if it is sort of permanent thing... probably add a panel.