I think that's a bad idea. The 200 f/2.8 with 2X TC is $1,000, 400mm f/5.6, 8 inches long, and mediocre image quality.

The 400mm f/5.6 is only $150 more, 2 inches longer, and image quality that is so much better it's not even funny. It makes the 200+2X combo look like a Fisher Price toy lens. As new, higher resolution bodies keep coming out, the disparity will only grow as the superior resolution of the 400mm f/5.6 gets utilized more and more.

If the white paint is a problem, then I would wonder if a black lens cover, tape, or paint would be a sufficient remedy.