I learned this tip from Walt Wright.
After assembly of your hive bodies / supers, and before painting, take a rasp and file off a small amount under the bottom corners. I just do the two opposite corners that could end up as the right rear corner as I keep the hive tool in my right hand. Hit it with sandpaper, and it's ready for painting. Now when I need to insert that hive tool between boxes, I have a starting point. This minimizes the damage done to the box that I sometimes cause when the squared corners are perfectly mated.