Congrats on the new call David.
Yes, you could use ADIF Master as Steve suggested. However, I didn't find it as easy as Excel in that I wanted to fill in one cell and do one copy/paste into thousands of blank cells. It won't do that. It will only paste the number of selected copy cells. Hope that makes sense. So it will take several copy/pastes for 7,000 records but still doable.
Or just start using your new callsign in the Operator field and assume if the Operator field is blank it is with your prior call.