If they don't DNW anything AU related, then you're fine making canon changes, although if it's the sort of thing that anyone reasonably familiar with canon would notice, you probably want to explicitly either tag it or A/N it if you don't want the anon memes talking about how badly you messed up canon and it must be kittyfic two months from now. (If it's, like, there's a five minute change in timing that you would only notice if watching with a stopwatch, you're probably fine.) If they have AU related DNWs it's trickier.

With a larger, major canon contradictory change like "Kirk and Spock are on Deep Space Nine with no explanation", I might also avoid it for a crack DNW just in case, even if you aren't treating it like crack (And similarly would avoid major character backstory/personality type changes for an OOC DNW, unless you do the AU work to justify them.)

(But like. If Kirk and Spock are playing dabo on Deep Space Nine they've clearly time traveled, it wouldn't have to be crack or AU.)