In theory, it's just a transfer, though I have heard of varying degrees of SNAFU perpetrated on personnel trying to go either way, or trying to reactivate from Sup Res.
There's now actually two options: transferring and re-badging CIC, or transferring in your current identity to the Cadet Organization Administration and Training Service: COATS. No idea what either'll do to rank, excepting you can't get promoted in your current trade as a non-CIC COATS member, though I suspect anyone ranking over Captain and looking to work with a corps in a paid capacity would need to do a voluntary reduction. With any luck, someone with more Pers experience'll be along soon.
What's the aim with this? Work with a corps? Find a home in one of the HQs?