This is acrylic paint brushed on O27 profile track on an ancient layout of mine from many years ago. As long as you don't really soak the joints with paint, electrical continuity shouldn't be a problem.
Tubular is hard to weather convincingly because of the rounded rail top. Either you leave the entire rounded part paint free (as I did) which leaves a large shiny rail top, or you paint it all, and then clean just the very top, leaving a very narrow shiny railhead.
The best way may be to paint the track first with a shaker spray can, taking the precautions Ace mentioned around the track ends. Then use a soft sanding pad to clean the top half only of the rounded railhead. It's tough to do that rounded top neatly, as you can see by the irregular paint job in parts of the photo.
Jim