You can copy and paste, but from my own experience it isn't that easy nor is it effective. Decals and other dynamic entities don't always paste properly, room walls get turned around or even upside-down, and other random stuff can happen that makes you pull your hair out.
Your best bet is to recreate the room from scratch. Go through each entity and write down what its coordinates are in the room (where it sits), and then drop them in the new room. This is easier than copying, pasting, fixing, and then starting over anyhow.
Priest of the Church of Joe Wood
In memory of Nanee. 9/1/1993 - 5/16/2009. Rest in Peace, little girl.