Hi,
Yes, it doable and not too hard, but need to decide if user can:
1. Manage this new check-box afterwords in his Profile, or have to unsubscribe or subscribe via regular side-box functionality.
2. Admin can manage this via User Record or it's better leave it as User Group management (when Admin needs to add/remove user from Subscribers group).
I personally think 1st one should be YES (allow to manage subscription status) and 2nd NO (keep it as is so Admin has to work via Add/Remove groups).
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Best regards,
Dmitry A.