Reject Traffic Unless Client has Certain Header or Client-IP

Try this and see if it works out for you. I did something similar for a Maintenance Override Page.

Create a Data Group List of IP Addresses:

- LTM -> iRules -> Data Group List -> Create -> Type (Address)

Replace Data Group List Name in place of "ListOfPeoplesIPAddresses" and add the IP Addresses of the Developers / Testors that you want to allow to override the iRule.

 when HTTP_REQUEST { 
if { !([HTTP::header exists "True-Client-IP"]) or !([matchclass [IP::remote_addr] equals $::ListOfPeoplesIPAddresses]) } {
reject
}
}