Dual ballast Ignition question.

Yup, you don't have to change a daid burned thing. A 4 pin ECU works just fine in a 5 pin system (but not vice-versa, as Cuda Al said)- the extra side of the ballast just becomes redundant, it's functions have been moved internally on the 4 pin ECU.
I always leave the double ballast and wiring in place, that way if I EVER have an issue I can plug in any ECU I have lying around, 4 or 5 pin, and get back on the road.