Does anyone know if Corsair tweaks their new cases after they've been out for a while?
Generally speaking, manufacturers will replace existing cases with newer ones rather than "revise" existing cases. The only exception, I can think of, is with USB 3.0 (some models are being re-issued with USB 3.0 on the front panel). The Corsair 550D already has USB 3.0, but I'm not certain what kind of connector it has (that is, does it pass through and connect to the back of the mobo, or does it have an internal connector?). If it is a pass through, it is possible Corsair could modify it to become an internal connector now that internal connectors are more prevalent.
Hope this helps.