Buttondown Documentation
Buttondown has the ability to let you give your subscribers the ability to change their metadata, tags, and more. This is called "subscriber autonomy."
When subscriber autonomy is enabled, subscribers can change their email address, name, and tags. They can also unsubscribe (or resubscribe) from your list:
To turn the setting on, go to Settings > Subscribing and toggle the setting labeled "Autonomy".
The forms displayed in the subscriber management page are the same as the forms you use to subscribe people to your list: subscribe form inputs. By default, these inputs only change a subscriber's metadata — but, combined with tags and automations, you can use them to give subscribers the ability to change their tags, too.
For simple cases, all you'll need to do is make sure to check the "Automatically tag?" input when creating a new Subscribe form input; this will ensure that, when a subscriber changes their metadata, the corresponding tags will change as well.
Some caveats: