I have a CUCM 5.1.x build connecting off to 8 to 10 CME/SRST routers in a lab build just now. The CME router has downloaded the phones with the command (srst mode auto-provision all) and flips over to these when the WAN link fails.
The problem i am experiencing is when a phone is deleted on CUCM, the CME retains the old settings. Then when you re-enter the MAC-Address the CUCM loads the old line/DDI details back onto the phone.
Does the CME router not update the ephone-dn/ephones if the CUCM config is changed?