There would be very little difference. There were less than 2,200 (~1,400 in 1943 and ~760 in 1944) He-111 built in 1943 & 44. Even if you make a one-for-one replacement the added capacity of the 217 isn't going to really change anything, the 217 simply wasn't that much better of an aircraft.
You would need the Do-217 to be a major leap in design (A5M toA6M, B-17 to B-29 or Bf-109 to Me-262) for a couple thounsand aircraft to have any sort of notable impact