Biodata contained information on a person's history and timeline (like 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 extract. 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 authorized to use (PROSE: Alien Bodies).
A Little Brother of Faction Paradox altered the Eighth Doctor's biodata to change his origins and to remove his ability to perceive the colour violet. The Doctor later fixed this change. (PROSE: Unnatural History)
Compassion evolved into a TARDIS after a receiver given to her by the Doctor warped her biodata by processing signals from the TARDIS as Block Transfer Computations that altered 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 - Book Two) Fortunately, the Doctor's TARDIS detected the change in the timeline and took the virus into itself, protecting the Doctor from its influence even as the future where he would succumb to the virus still existed, allowing him to eventually erase the timeline where he had been infected and died on Dust and restore his original third regeneration. (PROSE: The Ancestor Cell)