most manufactuer's instructions say to only apply/use above 40F. I gotta say, 40 is cold. I tried it once, and it was a pain. The wax dried slow, as did the water from when i washed it before hand. But to answe your question, yeah, its probably ok to polish, seal, and wax the car when its 50. Read the bottles though, most say in the instructions what temps you can use them in.
Polishes however, shouldnt matter the temp. They may be thicker and harder to work in the cold, but they will get the job done.