Mass Memory Alter

Mass Memory Alter is a Diamond spell that alters all the memories and records about a person on a massive if not global scale. Effectively altering the worlds perception of someone or something to hide anything that may be altered or changed by other forces. The Sorcerer (or caster) in question must concentrate on the mind of the individual(s) who is the epicenter of the spell and then reach out to sense and detect everyone who knows them to some degree. The caster will then build up a kind of humming mass of white (diamond) arcane energy that will take longer to build up to full strength based on the skill and power of the caster and how many people the spell will affect. Once at full power the spell will burst out in a load deafening boom. The spell will then instantly alter all memory, perception, and documented records of the individual it is epicentered on. The Spell is classified as Tier 4 in spell casting thus only sorcerers who continue past the more standardized magic schooling tend to learn it if at all. The standard Tier 4 spell book “Diamond Magi Adeptus Vol. 4” is know to contain this and other memory alter related spells. 
It is mostly used in the SF universe by Alistair Huntington and his protégés to alter all memory and records of individuals who they transform as a result of curing them of the Gender Curse thus there is little to no shock or confusion about those who have suddenly become another gender. The spell can be modified to not effect certain people when cast so that if the person at the epicenter has someone they trust or were close to before changing that person can retain their original memories if desired. There have also been cases where using the spell on smaller groups or with enough focus will avoid the deafening boom but there will likely still be a flash of white light to some degree. 
Based on the events of The King's Heirs it seems memories that have been altered with mass memory alter can be restored using magic to their original form, and some can even be left behind in an individual's subconscious and present themselves in the form of dreams. Sorcerers are immune to the effects of mass memory alter (and possibly all forms of memory alter magic) thus it is mainly used only in the non-Blood population to erase or rewrite memories to help conceal the existence of magic or avoid unnecessary issues when magic causes a change to certain individuals or things. The Spell usually is cast on masses ranging anywhere from several hundred to feasibly the entire planet but the larger the targeted population the more power and time the spell will require.
There are some cases of those who are at the epicenter of the Memory alter also being effected and having their minds altered to remember themselves as if the change done to them is normal. However its also been shown they their original memories can still resurface or appear in the form of dreams or intact instincts. It is also apparently possible to reverse the change done to them and as a result their original memories will begin to slowly come back to them. While other forms of magic can be used to restore those lost memories quickly but this can also have the side effect of causing the new memories since the original memory alter to be lost. By allowing the old memories to return slowly and naturally the person(s) in question get to keep their new memories without any issues.