If you read the story of Guy Gibson, he seems to have completed a tour (of thirty) and then gone on to fighter command, and then back to bombers. That was his choice it seems.
My father joined up in 1937 as an Armorer, became an Air Gunner but didn't go on Bomber Command ops until May 1942, first as an Air Gunner then Air Bomber. He competed his thirty by February 1943, went on various courses (Bomber Leader, Squadron Bombing Leader then seems to have become an instructor. In May 1945 he was back in an operational squadron, possibly preparing for Tiger Force, the attack on Japan.