No special configuration is necessary for the portion of the extension that extends the fe_user table.  

Minimal configuration is necessary, however, to use the modified template with the Frontend User Registration extension.  You can view full instructions on setting a custom template in the Frontend User Registration manual, available from the TYPO3.org Extension Repository.  The short instructions, however, are to go the Frontend User Registration section of the Constant Editor and locate the constant for the template.  The value of this constant can be updated to reflect the path of the template file within the WEC user extension.