There are different situations where a secondary breast reduction may be requested. One would be the young patient who may have had a reduction mammoplasty before she finished developing. Another may be the patient who gained weight after her original surgery and the remaining fat cells have grown larger. Then there is the patient who just wishes to be smaller than from the original surgery.
In most cases, a secondary procedure can be done. It is a little trickier, and close attention needs to be made regarding breast shape and blood supply of the nipple/areolar complex, which has been disrupted from the original surgery.
If the surgery is going to be done by a different surgeon, it is helpful to have the original operative report. Sometimes that is not possible, but it can still be done safely and efficiently as long as selection of the secondary surgeon is made carefully. Be sure to find a Board Certified Plastic Surgeon that specializes in breast surgery, ask a lot of questions and be sure to see before and after pictures of actual patients of the surgeon.