I was wondering whether it's possible to exclude a variable for one category, or a set of categories, where it is irrelevant. If not, would it be possible to consider such a feature? To illustrate this suggestion, it could be in the form of opt-out, (ie. all categories are included until excluded) or opt-in (ie. all categories are excluded until included) lists. This would be better than the current system, where only one rule for inclusion can be added. It would be definitely easier than creating multiple instances of the variable, especially with larger boards.

currently it's not possible, but from the looks of it the rework of the timing system will also include the feature you want,

although you could bypass it by making a new set variables for each category that needs em. gets a bit cluttered, especially w/ many categories/variables, but it works.

I'm still having this issue as of now as I'm wanting a variable to be set for all categories but one.

What made you think commenting on a 4 year old post would change anything? You can give feedback to the official new Speedrun.com feedback form: https://www.speedrun.com/knowledgebase/supporthub/give-feedback

For the record, I'm also waiting for this change.