So, currently I have a Mellon map in my car, and I'd like to go E85, with the tephra switch or whatever to switch between E85, and 93 Oct.

Question is, when I go get tuned at either Buschur or AMS for the E85 map, do I have to get a 2nd tune for 93 Oct also, since I'll be installing larger injectors/FP? Or would the Mellon Tune still be sufficient for the 93 Oct map?

 

You will still have to scale the injectors for you original 93 Mellon tune. Your fuel/timing maps will have to be tweaked a little, as well.