Bombardier stretched the CRJ-700 prototype twice, first to become the -900 prototype and subsequently that for the -1000.
Loftleidir returned some of their in-service CL-44Ds to Canadair in the mid-60s to have them stretched into CL-44Js.
Fokker, on the other hand, shrank the prototype 100 to turn it into the Fokker 70.