Just take your cat eye glasses back to the place where you bought them. Then ask the optician to make your cat eye glasses into sunglasses. They will have your lenses tinted just like sunglasses. However, you should ask them to add a UV coating to the lenses so that they can protect your eyes from harmful UV rays when you wear them outdoors. If you only add a dark tint to your cat eye glasses, they won't protect your eyes from the sunlight. But they will cause more damage to your eyes instead.
Yes, of course, you can. What you need to do is to get your cat eye glasses frames a pair of tinted lenses. Then, it will make you cat glasses into sunglasses suddenly. Now, most of optical shop offer tinted lenses varying in different colors like blue,rose, grey, brown, pink purple as well as black. You can choose any color of tint to your eyeglasses lenses to match your cat eyeglasses frames.