Currently, when you change the watching/tracking status of a category, it only applies that status to topics created from that point on.
If you watch a category and then a week later realize that’s too much noise and decide to unwatch it, you are still watching each individual topic that was created during that week. Manually unwatching each one individually is unintuitive and time-consuming.
There should be an option to apply the status to the entire category, not just new topics.
As long as it was an option. I would not want to turn on watching a category and have that applied unilaterally to every topic already in the category.
Here’s another thought … for something like changing watching to tracking, you might want to have the change applied only to the existing topics that are you currently watching. I.e. if you turned off watching for a topic, you probably wouldn’t want it to be set to tracking.
AFAIK the options for this use case are
Perhaps neither is ideal, but may be better than “Regular-izing” individual topics.
I think this has to be a pop up dialog that is triggered by setting the notification state for the category.
It should probably be something like
Category Notifications
You will begin watching any newly created topics in the bugs category.
Do you want to watch all 3,906 existing topics in the bugs category, too?
Yes, watch all No, just new cancel
So this would also let you reset watch state on a category, e.g. set all topics in that category to “regular” when you had it set to “tracked” for a few days.
I’m not sure if this is related, but it seems like something there should be an option to do or not to do:
Possibly, you may want to prompt about subcategories as well.
Bumping this feature request in light of the fact that I just now realized this is why some of my users weren’t getting notifications:
I wonder if instead of burdening the user with a choice regarding Watching all previous topics, if this couldn’t be a decision for the Forum admin? I presume that one of the reasons for having it only Watch new posts for users is performance related on large forums.
Maybe the admin could set an option that when the Watch option was selected on a category it also sets the user to Watch any topics that are NN days old. To simplify both the coding and the admin of the feature, I would be fine if it was a global setting and not a per category setting. So the UI drop down in those cases would read:
You will automatically watch all new topics in these categories and any topics that are NN days old. You will be notified of all new posts and topics, and a count of new replies will appear for these topics.
It seems to me that this could help more quickly on-board users into conversations as well. So they wouldn’t feel “left out” by not getting notifications on more recent topics that had active conversations they might want to participate in.
Just a reminder @sam it is looking more and more like we need to have this dialog on REMOVING the state from the categories – as we have safety code that prevents users from watching too many topics anyway, it’s the undoing / revert that is not handled.
I believe @sam will get to this early next week 
This is now part done per:
You can historically “unwatch” a category when changing.
However, historically “watching” / “tracking” opens a big can of worms. What if there are 700 thousand topics in a category, setting the read state can be crippling. It would have to have some limits.
I will add untrack tomorrow which should be fairly simple.
None of this stuff should be needed anymore, be sure to read the following carefully.