Just paint it. Before you spray paint on the temple of your sunglasses,you should pop out the lenses and cover the parts that go around lenses and the inside where the lenses were resting on with a tape of some type.Then you can spray paint them.
.Of course you can.If you want to buy them in a local optical store ,you just let the eye doctor test your eyes. Then the eye doctor will make glasses with your prescriptions and also the type of the sunglasses and clear lens.Or if you want to get them online,you must know your sizes and prescriptions when you select the sunglass frames and the clear lenses.
Many online eyeglasses stores can make prescription sunglasses for you. You can choose the frame that you like and then tell them your prescription. Then you can get a pair of prescription sunglasses a few days later or one week later. Why do you bother to buy a pair of sunglasses and then replace their lenses?
If you already have the glasses frame that you like at hand, you can take them to a nearby optical shop to ask whether they can replace the lenses for you. I know that some big eyeglasses stores will do that for customers while some small optical shops will not do that. And before doing this, you may need to have your eyesight checked and get a prescription if you don't have the prescription before. Remember that have your eyesight checked in the morning because our eyes are less tired at that moment so the result will be more accurate. Hope this helped!