Make members of a group watch a category by default

[watchmanmonitor (Allen Hancock)]

It’s worth noting that Watching a category doesn’t watch the category by default

it only watches the topic which are created after a member joins.

When changing category watch state, prompt to also change state of all topics in that category at the time of change

Yes – otherwise, the change affects only new topics, while you still won’t be notified to replies in old topics.