No, an admin cannot adjust a user's notifications. You can adjust the default notifications that are applied for all new members when they register, but there is no way to retroactively adjust either all members, or a single individual's notifications.
In the spirit of teaching them how to fish you could point them to this knowledgebase entry, or create your own for them to read.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .