In
Speaker for the Dead, Orson Scott Card uses the Portuguese term
descolada to name a disease that breaks the links of a being's DNA strand, leading to mutations in that being. It would not be too much of a stretch to use the term to denote magic that introduces mutations in reality - magic that takes the structure of space and time and, for lack of a more poetic expression, messes with it.
What would practitioners be called? Why,
descoladore of course. And if you don't like it, think of it as a starting point - right now I'm circling around a better idea based on this term but can't quite pinpoint it.
Later edit: Asmor had a good idea with the mathematical terms. I would also suggest:
1)
Disjunct magic - because your magic is different from ordinary magic, that works within the constraints of space and time, and because two sets that do not have any common elements are called disjunct, thus leading to a nice oxymoron in your definition of this class of magic.
2)
Aleph magic - from the mathematical notation of the smallest infinite set larger than the set of countable ordinal numbers. That is to say, that which is countably infinite (space and time in our example) is Aleph 0. That which is uncountable, such as the intervals in between space and time, is Aleph 1. I have yet to find a way to introduce the one in the above name in a satisfactory way.
P.S. Details about the math
here.