I have changed what we do with visitors' data. Can I ask everyone again?

Yes: Settings → How it asks → Ask everybody again. It asks you to confirm, and does nothing until you do, even opened in a new tab or from an old bookmark. Then everybody who has answered sees the banner on their next visit, with nothing ticked, and nothing optional runs until they answer. It empties your page cache so cached pages pick it up. It is not carried in a settings file, so pressing it on a staging site does not touch your live visitors. Save any other changes on Settings first: if there are some you have not saved, it asks whether to go on without them.