well... no... it wont be the same size.EDIT - there will be a FRACTIONAL difference. just make sure you sand uniformally and dont stay in one spot...otherwise itll reshape the body SLIGHTLY and yes, it will be smooth if you sand it right. once you get all that sealer off, switch to a higher grit paper, work your way up to like a 220 grit, take a wet rag and dampen the wood. This raises the wood fiber, sand that fiber off with 220 or 320 grit sand paper and repeat it once. After you do that it should be as smooth as bare would can get. I dont know what kind of wood that is.. but im not gonna go into sealer and grainfilling... theres whole tutorials on that..
BTW... if your going to use a translucent color, your gonna have to sand the sealer off to make it look uniform... but if your painting with solid colors, then you can just seal that one spot, spray a coat of primer, and it will be nice and even