Bob hope and no hope. It will never be a gemuine RS Turbo and trying to change the log book to say it is would be fraudulent on your part. It is an XR3i which has a turbo engine even if it had all the RST bit's it would still be an XR3i as that's how it left the factory.

Changing a Nova from an L to a pickup is a bit different as it has actually changed the body type.

You can get the log book changed for colour swap, Engine capacity and type but that is about it. As has been said even if you could change the logbook to say RST the VIN numbers would still identify it as an XR3i which would be even more off putting to potential buyers.