If our universe was fundamentally described by a theory of everything (let's say e.g. string theory) it would have a set of fundamental symmetries (which would correspond to the fundamental symmetries of that underlying theory of everything, like e.g. the fundamental symmetries of string theory). However, could there be any process or event where these fundamental symmetries would be broken (not spontaneously, but explicitly) or where they would not hold exactly (but only approximately)?
For example, if the universe underwent a vacuum phase transition, this could break the symmetries of the underlying theory, but only spontaneously (as far as I know), so the symmetries would actually still apply (at a fundamental level).
However could there be any other phenomenon or event (known in theoretical physics at least) that would change the fundamental structure and components of the universe so these fundamental symmetries would be broken explicitly (or at least would not hold exactly, but only approximately)?