As Huffy said, Proof can be changed without submitting new label approval. The only thing to consider here is that all you proofs fall within the allowable limit, IE you cant bottle whiskey at 60 proof and still call it whiskey, It has to fall within the allowable limits for that type of spirt but 80 proof on one bottle and 81.5 on the next one is allowable. You will have to keep this I'm mind when calculating your Taxes.