Perhaps it has something to do with "kerning"... manipulating the space between characters to force the 'r' and 'n' together to appear as something else. Now that I think about it, you can do the same thing in Word... take any misspelled word, set the kerning to 0 in the desired letters, and then copy-pasta (or find-and-replace) that word throughout the document.

So it's established that it CAN be done, but the question now is "Why?"