The Amtrak program has a nasty habit of eliminating redemption opportunities with minimal to no notice. Don't trust them. Move your points out of there as soon as they hit your account.
As I told a co-worker who is doing this, I would do the whole thing as quickly as possible, I fear that someone may pull the plug on this pretty quickly, though the AGR -> CP piece is the newest piece and possibly the one most at risk, I'm not sure if it would be Amtrak or Choice would might put an end to it (possibly by raising the redemption rate for CP points).