Where dome-head screws are used, it's perfectly reasonable just to grind or file them flush, assuming the base of the slot sits above the level of the langet surface. If you later decide to re-haft, you can either cut new slots (which might mar the langets) or use a chisel to split the haft. A nail works well for pass-through rivets. Some langet nails were long and narrow, and were automatically clinched by driving them through the haft against the opposite langet.