This is a good example of a thing you can pipe with royal icing that looks almost identical to the genuine article. You might wonder, why bother? But, probably obviously, the answer would lie in the taste. I'd definitely prefer crunching into a cupcake topper made of hardened sugar over flour and salt, wouldn't you? All you'll need to pipe pretzels are parchment paper squares (or a sheet of parchment taped to a cookie sheet), white and brown royal icing fitted with round tips #2 and #8 respectively, and a dusting pouch filled with a 50/50 mix of cornstarch and powdered sugar.
…then "salt" them with tiny shots of white icing, using the #2 tip.