If a group customizes their join form, will existing members be prompted to fill it out the next time they log in to Chezie?

Creating or updating a join form will not prompt existing members to rejoin. However, you can invite them to resubmit or update their existing forms. Existing users can do this by going to their user settings. On the page, they will see a button that suggests that they should update their join form because a new form has been added to the group.