(covers information from several alternate timelines)
Cosmetic surgery was a medical procedure to change the physical appearance of a person, frequently in order to deceive others of the altered individual's true appearance during undercover situations, such as reconnaissance missions. It had some of the same external effects as genetic engineering.
Known cosmetic procedures
In 2151, Jonathan Archer, T'Pol, Trip Tucker, and Hoshi Sato were surgically modified to look like Akaali while they investigated a disease on their homeworld. Archer later discovered another false Akaali when he removed the prosthetics from a face of a Malurian agent. (ENT: "Civilization")
In 2267, Captain James T. Kirk and Spock of the Federation starship USS Enterprise traveled back in time to 1930, and to explain Spock's alien appearance, claimed that a missionary had to use plastic surgery skills to save Spock's life after a mechanical rice picker accident, with the unfortunate side effect of pointing his ears. (TOS: "The City on the Edge of Forever")
In 2268, Arne Darvin, a Klingon Intelligence operative, was surgically altered to appear as a Human, but was identified during his mission to poison a shipment of quadrotriticale grain on Deep Space Station K-7. (TOS: "The Trouble with Tribbles").
Jadzia Dax also underwent a cosmetic operation to make her appear Human when, in 2373, the USS Defiant went back in time to stop a future Darvin from tampering with the timeline. (DS9: "Trials and Tribble-ations")
Later in the same year, Thelev, an Orion agent, was cosmetically altered to appear Andorian, planning to sabotage the Babel Conference concerning Coridanite's attempt to join the Federation. (TOS: "Journey to Babel")
In 2346, during the Cardassian Occupation of Bajor, Kira Meru was brought to Terok Nor to serve as a comfort woman to the Cardassian officers. Gul Dukat, the prefect at the time, noticed a large scar on her cheek. However, instead of having her replaced, he used a dermal regenerator to remove the scar. (DS9: "Wrongs Darker Than Death or Night")
In 2367, Riker underwent cosmetic surgery giving him the appearance of a Malcorian. He then went undercover on Malcor III to determine if the planet was ready for first contact with the Federation. Unfortunately, he was captured, and upon examination, it was discovered that he was not a Malcorian. (TNG: "First Contact")
In 2368, Captain Jean-Luc Picard and Lieutenant Commander Data underwent cosmetic surgery under the supervision of Doctor Beverly Crusher so that they could conduct an undercover operation on Romulus. (TNG: "Unification I", "Unification II")
In 2369, Troi was kidnapped and surgically altered by the Romulan underground movement to assume the role of Major Rakal of the Tal Shiar and help Vice-Proconsul M'ret and two of his aides defect to the Federation. (TNG: "Face of the Enemy")
In the same year, Aamin Marritza, a Cardassian file clerk, had some cosmetic surgery to impersonate another Cardassian, Darhe'el, in an attempt to be punished for not opposing crimes committed during the Occupation of Bajor. (DS9: "Duet")
A bit later, Commander Riker and Doctor Crusher had cosmetic surgery to appear like Barkonians and uncovered what happened to Data after a Federation probe crash landed on the planet Barkon IV. (TNG: "Thine Own Self")
In 2371, Entek of the Obsidian Order captured Kira Nerys and altered her to appear to be Legate Tekeny Ghemor's daughter Iliana in order to expose Ghemor's ties to the Cardassian Underground. (DS9: "Second Skin")
Around the same time, Arissa, the alias of an Idanian Intelligence agent, underwent reconstructive surgery and her memories were replaced in order to infiltrate the Orion Syndicate. Two years later, Odo revealed her true identity. (DS9: "A Simple Investigation")
In 2372, Dr. Bashir erased the memory of Kurn, Worf's brother, and surgically altered his face so that he could assume a new identity as Noggra's son Rodek rather than be killed by Worf. (DS9: "Sons of Mogh")
In 2373, a Starfleet team infiltrated the Klingon station Ty'Gokor in an attempt to expose Chancellor Gowron, the leader of the Klingon Empire, as a Changeling. The team was comprised of Worf, Benjamin Sisko, Miles O'Brien, and Odo. The latter three, not being Klingon, had to undergo cosmetic surgery. Upon arrival, they were captured when General Martok recognized Sisko. The team later realized that it was not Gowron, but Martok who had been replaced. (DS9: "Apocalypse Rising")
Later on, Neelix was cosmetically modified to look like a Ferengi, and portrayed himself to be the Grand Proxy in an attempt to convince Arridor and Kol to relinquish their hold on Takar II. (VOY: "False Profits")
In 2374, Quark agreed to have his gender and appearance altered by Doctor Bashir to convince Nilva, chairman of Slug-o-Cola, that Ferengi females were intelligent and deserved certain rights in the Ferengi Bill of Opportunities. He was later changed back to a male. (DS9: "Profit and Lace")
In the same year, a pack of Hirogen ships successfully claimed the starship USS Voyager and forced some of the crew to participate in vast holodeck hunting simulations. Certain personnel were surgically altered to appear like Klingons, including Neelix and Captain Kathryn Janeway. (VOY: "The Killing Game", "The Killing Game, Part II")
In 2375, Damar arranged for Dukat to be surgically altered into a Bajoran. Under the false identity Anjohl Tennan, he gained the confidence of Kai Winn Adami in an attempt to free the Pah-wraiths from their prison. (DS9: "Penumbra")
Later that year, Neelix used a dermal regenerator to create a "pretty authentic" plasma burn on Seven of Nine to try and deceive the series 5 long-range tactical armor unit who suppressed The Doctor's programming and took control of his holomatrix. Neelix touted himself as the "chief cosmetics officer", to which Tom Paris said that maybe the captain would promote Neelix to "senior beautician". (VOY: "Warhead")
In 2377, most of the stranded crew of Voyager was captured and brainwashed. The crew was then put to work on the planet Quarra to compensate for a labor shortage. The Doctor cosmetically altered the appearance of Chakotay so that he would be able to enter the planet without arising suspicion. Unfortunately, he was captured and identified while trying to rescue Torres, who was nearing the end of her pregnancy. (VOY: "Workforce")
Shapeshifter races usually had the ability to manipulate their entire physical state and appearance as they saw fit. These included Odo and other Changelings, races like Chameloids, Allasomorphs, and individuals like Garth of Izar. (Star Trek: Deep Space Nine; TOS: "Whom Gods Destroy"; Star Trek VI: The Undiscovered Country; TNG: "The Dauphin")
After Seven of Nine was torn from the Borg Collective in late 2373, The Doctor restored most of her Human biology and appearance, but she still had some visible Borg technology left behind. Further attempts to remove the last of her Borg implants proved hazardous to her health. (VOY: "The Gift")
In 2376, The Doctor had his program modified so that he could appear like the inhabitants of a planet rotating 58 times per minute and determine if there was a way for Voyager to escape its orbit. (VOY: "Blink of an Eye") In 2378, The Doctor maintained the ability to copy the outer appearance of others by downloading their physical parameters into his holomatrix. (VOY: "Renaissance Man")
Later in the same year, The Doctor used medical techniques to begin transforming Ensign Lyndsay Ballard, who had been killed during an away mission and resurrected by the Kobali, back to Human form, including her hair. (VOY: "Ashes to Ashes")
Cosmetic procedures and technologies
- Colgonite astringent
- Dermal regenerator
- Dermal stimulator
- Dermatiraelian plastiscine
- Lobe enlargements
- Species reassignment protocol
- Tooth sharpener
(Referring to tribbles)
"They don't like you, Mr. Darvin! I wonder why? Bones?"
(Scans Darvin with tricorder)
"Heartbeat's all wrong... blood pressure is– Jim, this man is a Klingon!"
"Be careful, android! Some Romulan beauty might take a liking to you! Lick that paint right off your ears."
"This is not going to work. It is not enough to look like a Klingon, one must act like one. Perhaps it would be better if I went by my..."
(Sisko backhands Worf across the face)
"Are you questioning the validity of my plan?!"
"Very convincing, Captain. But was it your intention to challenge me to a battle to the death?"
"No, not at all."
"Then next time do not strike me with the back of your hand. Use your fist."
"The Doctor thought I should stick to my original [hair] color, but this seemed more exciting."
"Hair is one of my specialties, despite evidence to the contrary."
The comic book series Star Trek: Khan set in the alternate reality establishes that Khan Noonien Singh was surgically altered by Section 31 after being discovered and given a new identity as John Harrison, explaining how his appearance differs from his Prime Timeline counterpart.