A former President of the Homeworld could be known as Lord President Emeritus. (PROSE: The Bloodletters)
Presidents Emeritus retained their metaphysical connections with the Protocols after their time in office. During the War in Heaven, these connections became a liability, and many Presidents Emeritus resorted to faking their deaths or disappearing; (PROSE: Sabbath and the King) the Doctor was one former Lord President (PROSE: The Eight Doctors, et al.) who superficially seemed to die at the start of the War, (PROSE: Alien Bodies, The Book of the War) while the War King was an example of a President Emeritus who simply disappeared. (AUDIO: Sabbath and the King, Words from Nine Divinities)
When the Monk told the Corsair about the death of "the President Kodachrome" in the Ghost Wars, he referred to him as "the Lord President Emeritus" as well as "the President-Who-Would-Not-Serve". (PROSE: The Bloodletters)