XF 2.3 User must select Custom Field

[htsumer]

I've added a special field for users. New members are required to select it, but existing users are not. I don't want existing users who are missing this special field to be visible on the forum until they fill it in. I don't want existing users to be able to proceed with the forum without completing it. After completing the special field, they can continue accessing the forum.

 

[Lee]

Create special field.
Remove required permissions from the Registered group to prevent the access you want.
Create a new user group to reinstate those permissions once upgraded.
Add a user group promotion based on the special field making sure you add the user the new user group with extra permissions upon upgrade.
Run the cron manually to apply the upgrade to current users who meet the criteria, unless you are willing to wait until it is triggered.