Users that might customise their system a bit by digging into the settings are usually more inclined to give a detailed report in case they encounter a bug or have a general knowledge of what to look for when requested for some information in my team's experience. Sounds much more like an edge case.

True, but if the policy is to reject all cut screenshots... I'd rather add an "unless the ticket contains all the relevant information".

Most users don't customize anything, even something as trivial as that. Most corporate users may not be allowed to. I bet they never had to deal with any of these supposed gotchas.