What happens in the Zendesk Agent Workspace when an end-user enters their name in the pre-chat form and it differs from their user information that already exists in Zendesk Support?
When a username miss-match occurs between what they entered in the pre-chat form and the information that already exists in Support, Support will always choose the requestor's name that already exists in the user profile in the Agent Workspace.
End users are only able to change their user name when they have authenticated into the help center and edited their user profile. Otherwise, anyone who fills out a pre-chat form can use any email address and pretend to be someone else.
Note: When there is a disconnect between the names in the pre-chat form and the Support user profile, a yellow notification popup appears in the customer context. The notification, "Some contact details provided in this conversation don't match user profile" will then state what is different between the users, like the user's name.
For more information on how agents or end users can edit user profiles, see the articles: Editing your Help Center profile and Adding end users.