If you have a fully redundant internal BGP, and are running all 12.2S/12.3/12.2T, then you can rather safely do the internal BGP passwords without a customer notice, expecting no session drop but knowing if one did you'd have routes via a second BGP reflector anyway.

Just an FYI, when we changed sessions that had full routing tables on them at 2am CST with barely any traffic, it causes malloc failures on the Cisco 7513. So it's something I would reserve for a maintenance window if you have one.