The various arcane backgrounds won't be majorly changed, however there are a few minor notes that I thought I would add to each.
Arcane Background: Magic
Magic is subject to control and regulation by the MCB. Magic use regulation involves educating the subject on the specific laws regarding magic use (never in public, never on a large scale, NEVER ANY SORT OF NECROMANCY), as well as a period of working for the government in some aspect while under heavy supervision (where depends on what spells or talents a spell caster has, always well paid). People who know how to cast spells, but haven’t been found out by the government, are almost always either extremely lucky or extremely cautious, but are not entirely uncommon. In places like New Orleans where there are many with the gift, the MCB doesn’t actively hunt them down unless they make themselves noticed. Necromancers have an unpleasant tendency to come back from the dead as some sort of undead.
Arcane Background: Miracles
Miracles represent powers and abilities granted by extremely powerful, other dimensional beings who like to meddle. They are subjected to the same sort of scrutiny concerning spell casting as normal magic users, as well as by what amounts to constant supervision by their divine source and related church. In this game there are three primary sources of Miracles: Heavenly, Fey, and Outsiders.
Heavenly represents a divine power that are typically most interested in the best for humanity and countering the plots of evil. Typically organized along various earthly faiths (religious conflicts are a part of the divine plan). Heavenly is the only power source that can create holy water.
Fey represent a more wild, elemental divine being. Their interests mainly involve protecting wild spaces and things, and pretty much doing what they want. The Fey are organized along various pagan religions, and seemingly fight with each other as much as they have conflict with anyone. These miracle workers are also the most circumspect and work hard to avoid drawing attention to themselves.
Outsiders represent what would be considered as evil divine powers, whether Lovecraftian space fungus or fallen angels. These powers will lie and cheat their mortal worshippers in order to draw more of themselves onto this world. Outsiders freely teach necromancy, encourage human sacrifice, and always leads to loss of sanity by their mortal pawns. These powers virtually never have much in the way of organization, and a leader typically dominates other casters through the capricious whims of the higher powers they follow, as well as by whatever violence is necessary to maintain their position. Outsider miracle wielders, much like necromancers, tend to come back from the dead as some sort of undead.
Arcane Background: Psionics
Psionic power wielders tend to make their powers very secret, as it is rumored that the government dissects psionic wielders brains to duplicate their abilities. This is very likely true. The MCB certainly actively scouts out psionic individuals (as much as they’re able to), in order to put them through a similar type of program as magic wielders, though those who completely wash out of the program are generally lobotomized. The government is worried that there is some evidence of other dimensional powers being able to contact psionics wielders, for no doubt nefarious ends.
Arcane Background: Superpowers
People with superpowers are the rarest form of arcane background, and the MCB lacks any kind of reliable way to detect superpowers other than seeing them directly. The few found by the MCB are typically explained away as an escaped experiment (magical, alchemical, weird science, etc.), alien influence, or some sort of crossbreed with unnatural critters.
Arcane Background: Weird Science
Weird science is probably the most common of arcane background, as every town or city has some sort of bizarre tinkerer in residence. The government, in an attempt to advance sciences, actively cultivates a number of organizations to help or support inventors considered to be weird science, in an attempt to monitor and control explosive technological growth, as well as fight communist influence.