Rule 8.2.1 allows any owner to apply for a second valid IRC certificate for their boat. The Secondary certificate allows for certain configuration changes, with potential applications being inshore/offshore; shorthanded/crewed; racing/cruising sails; or even a specific configuration for a single event.
There are limitations on the data that may differ between the primary and secondary certificate; this is generally limited to sails, certain rig data, use of stored power; and use of moveable, variable or internal ballast.
A Secondary certificate is only available to boats holding a current, valid primary certificate.
For full details see Rule 8.2 in full in the current version of the IRC Rule text.
The application form to apply for a Secondary (SEC) IRC certificate can be obtained from your Rule Authority.