A Mary-Sue was a process that an individual elected to have done. It wiped the individual's mind, then rebuilt a wholly new person in its place. A Mary-Sue was also the process of placing a new personality profile on top of an existing individual's personality. This process was reversible.
Bernice Summerfield underwent a Mary-Sue to protect her mind from the All-High Gods on Dellah when she returned to retrieve her cat, Wolsey. The process that Bernice underwent was reversible. (PROSE: The Mary-Sue Extrusion)