Go to the local hardware store and buy the paint scraping tool that has a round side to use to scrape the paint off a roller. They are usually quite thick, and sharpened, and designed to be hit with a hammer. If you do any painting around eh house you may already have one..
Yes, used improperly they will ruin both sides of your seam. You need to do something to make the one side weak, so it breaks off the good part. Either grind partly thru the welds or use a spot weld cutter, or work on something that is really rusty on one side of a seam. You'll be a pro after the first 200 or so spot welds anyhow.