This is a "what if" so different choices can be made but they would have had to have been made at appropriate times in order to take effect.
14th May 1939, first flight by Short Stirling.
25th July 1939, first flight by Manchester.
13th August 1939, first flight by Warwick.
25th October 1939, first flight by Halifax.
25th November 1940, first flight by a Mosquito
8th September 1941, first flight by Mosquito MK IV bomber.
9 January 1941, first flight of the Lancaster. And that went on to become the mainstay of BC. Had they wished to change approach, it could have been done. Not to mention that with the appalling loss rate (IIRC around 7% on average, meaning a heavy bomber lasted on average only about 10 missions before being shot down) they needed to produce a huge number of them just to keep the fleet numbers up. With the much lower loss rate of the Mossie (or something similar), a correspondingly lower rate of production would have been needed to keep the force numbers.