You should get in writing from your insurance company that the "pre-approval" for your browlift applies to a different surgeon. If they do not provide that for you, you should get re-approval with the new surgeon.
As far as insurance coverage for browlift goes: it is a tenuous proposition. Sometimes they do and sometimes they don't....even when you have the so-called "pre-approval". Furthermore, the reimbursement they provide is extremely low compared to the amount of work a surgeon needs to do for a hairline, endoscopic, or coronal browlift. These are significantly more complicated procedures, and are much more difficult to get the desired lift a brow needs for a functional need [to improve vision]
For these reasons, most surgeons would only do a 'direct' browlift, which means the incision is directly above the eyebrow in the forehead. Although, with time, this heals well, there will be a scar visible above the eyebrow. This is a more effective technique in elevating the eyebrow for functional reasons, but it is not the most cosmetically ideal incision. But then again, if the surgery is being paid for by insurance, cosmetic incisions shouldn't be used, right?
Good luck