Option, if you are only worried about the flaring die, take a scratch awl scribe a line on the lock ring when setup for 38 special. On the die threads put a dab of nail polish lined up with the scribe, then set the die for 357 and put another scribe mark on the lock ring corresponding to the dab. You now have a rough in adjustment switching between the 2. Pain yes, but quick.
Other option is dedicated die set.
