Cosmetic surgery

Cosmetic surgery, also known as plastic surgery, was a medical procedure to change the physical appearance of a person.

In 2155, Charles "Trip" Tucker underwent cosmetic and genetic surgery to appear as a Romulan. 

In 2266, James T. Kirk had Dr. Dwayne Stiller make his face temporarily look like a Dridian so he could investigate the criminal charges against him. 

In 2270,, a duplicate of Kirk, was surgically altered to pass for Romulan.