A poster did a test a few months ago…. Two people traveling & the price dropped close to the flight. She repriced 1, did not reprice the other. They still had consecutive numbers, just as they normally would have.
I think if you change due to a price drop, you’re fine & keep your spot. If you change to a different flight, that’s when you’ll lose your place in line. You’ll still have EBCI, just in line behind others on that flight who bought it before you moved. Which I think is fair. I would hate to buy EBCI months out, then have a price drop a few days before the flight that leads to several people moving to my flight with earlier dates & push me far down the check in list.