It's fine if it's a genuine variant of the name (i.e. Carl, Karl, Carlos, Charles, etc.).
"Jon" is not a variant of "John," it's a shortened version of "Jonathan," an entirely different name.
But if you're talking about altering the spelling of an established saint's name for the sake of being "unique" (i.e. "Klarees" instead of "Clarice" or "Antonee" instead of "Anthony"), well then... you might just be a redneck.