Mix mayonnaise, mustard together with salt and pepper. Mix thoroughly, until yolks are like a spread, no crumbles. Mix with pimento cheese.
Taste for heat, salt, and mayonnaise. Add only as needed. Put into a pastry bag fitted with a large 1 M or star tip.If you don't have, use a plastic bag and cut a very small hole in one corner.
Slice lengthwise and empty yolks into a bowl.
Squeeze mixture onto eggs. Refrigerate covered, by placing in a large baking dish.