On our Skagway shore excursion to the dog-sledding camp, our tour guide told us that the town was originally called Skagua, a Tlingit word meaning "windy place," but the post office misspelled it at some point, and from then on, the y stuck. Nice!
A Skagway tour website adds a bit more to this tidbit, how the name started off as Skagua and then was changed by a surveyor to Skaguay, and then: "Spelling changed to Skagway by post office, and most businesses reluctantly follow. Townspeople are called Skagwayans."
If a misspelling or invented/evolved word makes it into mainstream publications frequently enough, it will eventually be recorded into the dictionary. Heck, I bought the 1995 edition of the Random House Webster's College Dictionary because it contained the word womyn!