This school of magic allows past events to be changed to mesh with current needs. It is theorized that only the Titans have access to the powers of Retconjuration as it is too powerful for a mere mortal to comprehend even its smallest of ramifications. Being a very volatile subject, it is usually avoided in most public forums and viewpoints on the subject differ greatly.
Mortal users of Retconjuration would be in position to engage each other in a war of existential reconstruction, up to the point that only a timeline where they were all erased would be stable. Of course, as there have been no mortal Retconjurers, this is not possible.
(alternatively, perhaps there is one final retconjurer at the end of time, who will haven retconned all previous ones into nonexistence)
Things that have been Retconned
The school of Retconjuration is notable for being an example of itself; the Numbers axis of Naughtymancy was an entirely different school called "Deletionism" the-ultimate-naughtymancy until the Titans realized that Retconjuration would be necessary for them to properly maintain Erfworld. As a removed school of magic, this also kind of makes Deletionism an example of itself.
One line of fan speculation postulates that there could be a Retconjuration war going on between the Titans, with one faction backing Stanley the Tool's bid to overthrow royalty and unite the Arkentools, and the other opposing it. So far, the side opposing Stanley has left an extra gem in a Marbit mine, leading to Stanley's defeat at the Battle of Warchalking, and the other has caused Lookamancers and Findamancers to research the "Summon Perfect Warlord" spell, or possibly provided Parson's glasses, bracer and sword, leading to the defeat of the RCC.
The name refers to "retcon", short for "retroactive continuity", in which the history of a fictional setting is be changed after publishing to mesh better with the current desires of the author. This is ironic because this form of magic is itself a retcon.