Whisk whiskey, cider, sugar, 2 teaspoons vinegar, mustard, vanilla, and cayenne together in bowl. Transfer 1/4 cup whiskey mixture to 1-gallon zipper-lock bag, add pork chops, press air out of bag, and seal. Turn bag to coat chops with marinade and refrigerate 1 to 2 hours. Reserve remaining whiskey mixture separately.
Remove chops from bag, pat dry with paper towels, and discard marinade. Heat oil in 12-inch skillet over medium-high heat until just beginning to smoke. Season chops with salt and pepper and cook until well browned on both sides and a peek into thickest part of a chop using paring knife yields still-pink meat 1/4 inch from surface, 6 to 8 minutes, flipping chops halfway through cooking. Transfer chops to plate and cover tightly with aluminum foil.
Add reserved whiskey mixture to skillet and bring to boil, scraping up any browned bits with wooden spoon. Cook until reduced to thick glaze, 3 to 5 minutes. Reduce heat to medium-low and, holding on to chops, tip plate to add any accumulated juices back to skillet. Add remaining 2 teaspoons vinegar, whisk in butter, and simmer glaze until thick and sticky, 2 to 3 minutes. Remove pan from heat.
Return chops to skillet and let rest in pan, turning chops occasionally to coat both sides, until sauce clings to chops and meat registers 145 degrees, about 5 minutes. Transfer chops to platter and spoon sauce over. Serve.