you will need to edit the Insert Record Behavior on the registration page using DataAssist to bind the new form element to the new database column.
With DataAsisst installed, open the server behaviors panel, Window -> Server Behaviors, then double click the insert record server behavior to edit it.
Dont change anything on the first page, click the next button, on the second page, select the database column, then click the lightning bolt icon next to value and select hte new form element.