When does admission to major after enrolling become a concern?

Doesn’t it depend on the major? If it’s something like engineering, where you’re either in or you’re out, I imagine it’s a big concern.
If it’s something like my daughter’s case - where the major is honors-only and requires a 3.6 minimum GPA, but is also a major that can be mostly “cloned” through the right course selection - then it’s less of a concern.