Depends how much out of balance they are, if there close to balance then I just apply extra coats of paint or clear to the light blade, or if it's way out of balance I'll consider scraping it, or for out of production props I’ll sand with 400 grit wet n dry to the front of the heavy blade, and then do the paint or clear method. I try and avoid touching the back of the blades as it's easy to change the pitch unintentionally.
Mike.