This is not exactly the same as the editors of a journal changing the publisher of a journal, but let me put in a plug for "flipping" a journal to Open Access. This is where the editors of a journal (which is presumably published by some for-profit publisher) all simultaneously quit in order to found a new open access journal with the same scope, same editorial team, and similar name to the old one.
Some recent examples I know of this happening in math -- and specifically, combinatorics -- are:
- Algebraic Combinatorics, which flipped from "Journal of Algebraic Combinatorics" (see this press release, Inside Higher Ed article, Europ. Math. Soc. newsletter article)
- Combinatorial Theory, which flipped from "Journal of Combinatorial Theory, Series A" (see this press release)