Would like to be able to change the user name/email once they’re added to a board. It’s a small nitpick, but I would like to tag a user (e.g., @Joe) instead of the full email address (@joe@website.com).
Hey there Mat 
Welcome to the community, we are happy to see you here 
Since each individual user creates its own account, it would be hard to manage / change or edit their email addresses or names. Currently you can mention (tag) users by using the @ sign and typing members name.
So, lets say you have 2 colleagues who are named John, once you type @john you will get the drop down menu to select which one you want to mention / tag: (example image with name: “Marko”)
However, thank you for your suggestion, we would also like to encourage you to suggest it via this FORM so that other users can vote for it, it will help us understand what our users want and need 
Thank you @matt5 