Of course, regardless of your liver or thyroid status, if you were in a car wreck and needed surgery to save your life, then there is no question about the appropriateness of proceeding with necessary surgery. The risks are higher than NOT proceeding.
But with elective cosmetic surgery, taking on unnecessary risks becomes another thing entirely!
Your internist or family practitioner should evaluate WHY your liver enzymes are elevated (how much is another issue), as well as identify the cause and proper treatment for your thyroid issues. More testing may be needed, and the driving force here should not be the timetable of your scheduled elective surgery, but your overall health and suitability for anesthesia and elective cosmetic surgery. THIS is why patients are required to have a complete medical history, physical examination, and lab tests PRIOR to undergoing surgery (especially elective)--we want to ensure as much safety as possible.
Anything less is foolish. Follow up with your own physician, and reschedule with your plastic surgeon if necessary--he or she will certainly want what's best for your overall health. (We prefer our patients to be out walking around and showing off our good work and results, rather than just looking good in the casket!)
Elevated liver enzymes may simply be related to the party you were over-served at last weekend, or medications you take, or could be a sign of other more serious issues. Don't ignore this; don't seek reassurance on-line; go see your doctor! Best wishes!