There is an attribute extension that is available to be added for registrant records that adds an Event Registrant Attribute tab to registrant records. One of the attribute record types that can be added is the data type of "Constituent record." This allows users to search for and select a constituent record as the attribute value for the record. The ability to edit this attribute can also be added to the extended onto the "Edit registrant" form. While users are able to search for and select constituent records for attribute values on the Attributes tab of the registrant record, non-system administrators will receive 0 results if they attempt to search for a constituent record for an attribute value from the "Edit registrant" form. The search returns results successfully from both locations if run as a system administrator.