The torpedo dropping requirement in Spec P.13/36 that led to the Manchester was dropped on 26 Aug 1937, long before it ever flew or the Lancaster was conceived. Other elements dropped before the Lancaster was conceived were:-
The catapult launch requirement was dropped on 4 July 1938. However it seems that the weight saving this should have generated could not be taken advantage of in the first 20 Avro Manchester airframes as they were already on the production lines, and it is not clear if it was ever designed out, according to Robert Kirby's "The Avro Manchester". Why the weight saving from this and not the dive bombing requirement is specifically noted in more than one book I know not. It is also odd that the first production Manchesters did not come off the production line until July 1939, if 20 were already on it in July 1938.
The dive bombing requirement was dropped on 11 Aug 1938 as the 60 degree angle required was considered unobtainable.
The troop carrying requirement also in the original specification was not dropped until 30 January 1940.