With most chains. For example, with Starwood you can only get a comp to Platinum if you've never been platinum before (they won't comp you even if your previous platinum was earned). However you can get re-refered over and over to Intercontinental Royal Ambassador status, at least as of a couple months ago. (I was referred in December '05, my status expired at the end of December '06, and I was bumped back up to complimentary RA status in January '07 via another referral cert.)

Intercontinental Royal Ambassador status always lasts until the end of your current Ambassador membership. If you aren't currently an Ambassador they'll sign you up and it lasts for 12 months. If you have less time left, renew your Ambassador status and then (or concurrently) send the referral. I suspect it might be possible to get the status for, say, 15 months this way -- but go to the Priority Club forum and research royal ambassador referrals first...

Starwood is the most interesting case. Their status always lasts at least 12 months, and status expires Feb 28. So if you get comped to Platinum after March 1, it can't expire Feb 28 of the following year -- 'cause status would have lasted less than 12 months -- so it lasts until Feb 28 of the NEXT year. Example: if you took a comp today (March 30, 2007 in the U.S.) then your status would expire February 28 2009.