High sodium diet soon after tummy tuck will make your body retain more fluid. You may retain fluid longer after tummy tuck. However, it will not affect long-term tummy tuck outcome. Obviously, you do want to keep a healthy diet after tummy tuck so that you do not gain weight and maintain your body healthy.
If it is a sudden change from a healthier sounding diet there might be a bit more swelling, but in the average person, particularly if this is not a dietary change, probably no affect.