Can we stop a record being found in the directory if we use first name rather than preferred name?

Summary:

We have changed all the name formats to preferred name and last name rather than first name. However, when we go to the directory and type in a first name, records are returned even though the person's first name does not match this search. Can we stop this.

Content (please ensure you mask any confidential information):

We are looking to be move to all screens in Oracle displaying people's preferred names and last name rather than first name, last name (preferred name). This is in response to the equalities act.

As a HR and Payroll user we still need to be able to search for people by their first name so that we can respond to documentation we may receive from third parties, but other users should not be able to see the person first name on any screens.