I just submitted an I-D on TCP-MD5 key change. Until it shows up in the official repository, see http://www.cs.columbia.edu/~smb/papers/draft-bellovin-keyroll2385-00.txt Here's the abstract:
The TCP-MD5 option is most commonly used to secure BGP sessions between routers. However, changing the long-term key is difficult, since the change needs to be synchronized between different organizations. We describe single-ended strategies that will permit (mostly) unsynchronized key changes. Comments welcome. --Steven M. Bellovin, http://www.cs.columbia.edu/~smb