Will I remain the same weight after surgery for hyperthyroidism?

Maybe. Depends on how long you have been hyperthyroid and how much weight you have lost because of it. Once the surgery is over, you will be placed on thyroid homone which will get your level back to the normal range. If you have been "artificially" accelerated by the hyperthyroidism, you could gain some weight back to your natural level (how you were supposed to weight). Diet/exercise can limit this.