Biodata (short for biographic data) contained information on a person's history and timeline, analogous to temporal DNA. If a person's biodata could be manipulated, his entire time stream could be altered. (PROSE: Alien Bodies) A biodata signature was also referred to as an "artron imprint." (AUDIO: The Inquiry)
On Gallifrey, there were stores of all Time Lord biodata in the form of biodata extracts, called biogs (short for biodata log). Excitonics was the technology underlying its circuitry. The Master was able to gain access to the Fourth Doctor's biodata extract to summon him to Gallifrey. (TV: The Deadly Assassin) Certain artefacts could also alter biodata, such as the Sash of Rassilon and other Presidential artefacts changing the biodata of Time Lord presidents to allow them to access certain secrets that only the President was authorised to use (PROSE: Alien Bodies).
Griffin was able to alter the Eighth Doctor's biodata to remove his ability to perceive the colour violet. Griffin also prepared a pair of formulas that would alter the complex biodata histories of the Doctor and Samantha Jones into a single more predictable timeline, but the Doctor and Sam destroyed these samples before they were forced to drink them. The Doctor later claimed to have fixed Griffin's 'tweak' regarding his ability to see violet, (PROSE: Unnatural History) though much later in his life, while suffering from amnesia with no memory of these events, he again professed his blindness to this shade. (PROSE: To the Slaughter)
Compassion evolved into a type 102 TARDIS after the Doctor added a filter to the receiver she had been given by the Remote (PROSE: The Blue Angel). The filter was intended to prevent Compassion becoming susceptible to any random signals she would pick up in her travels with the Doctor, but the filter resulted in Compassion's biodata becoming warped as the filter's link to the TARDIS resulted in Compassion's receiver processing signals from the TARDIS as Block Transfer Computations, altering her physiology. (PROSE: The Shadows of Avalon)
The Faction had developed biodata viruses that could infect potential Faction members to convert them to share the Faction's beliefs and abilities. Normally these viruses were too weak to infect Time Lords, but the virus was able to infect the Third Doctor when his history was changed and he was killed on Dust, resulting in him regenerating ahead of schedule and the virus infecting him while his immune system was in chaos during the change. (PROSE: Interference) The Doctor believed that he could cure himself of the virus with access to samples of his uncontaminated biodata, but he never had a chance to test this theory, and was only able to save himself by averting the timeline where he was infected in the first place (PROSE: The Ancestor Cell).