I had my painter paint my bathroom walls two colors with semi-gloss paint: a federal blue on top and white on the bottom. Colors are separated by a white chair rail. The paint looks too thick (sort of like orange peel) especially on the bottom half. I want to do the picture frame faux wainscoting on the bottom half but would like to lightly sand the walls to make them look better without repainting. Would that be possible?

As I mentioned, the walls are two colors. I am thinking, now, maybe I should paint the lower half a little bit darker than the top because the picture frame moulding is going to be white.

I have included a picture.

Any suggestions?