Option to be able to opt out per catagory

I am having a number of catagories on my site. Two to contact a specific role, I do not wish to make optional, yet the all user list (for authenticated users) I wish to allow people to opt out of. The only selection I can find for it seems to be for all the categories, thus I cannot get this to work as desired. Certain roles on my site are elected positions, so for those positons, I would prefer to not allow a choice for the emails, but the all user list I would like to allow a choice, for someone who is not a part of the organization anymore needs some way to cancel the emails coming to them.