As far as the iSCSI address change is concerned if you have changed the ip-address of the vmkernel port you are using for iSCSI then for ESX 3.5 you will have to reboot the ESX host otherwise things will get unstable. That's if the change refers to the iSCSI Software initiator on the ESX Server. If that hasn't changed and you just want to change the iSCSI target address the initiator is pointing to then just change the properties in the initiator [Config Tab, Storage Adaptors, iSCSI Software Initiator, Dynamic Discovery, Add Send Targets Server] to point to the new iSCSI target address. Again a reboot is strongly recommended, the ESX 3.5 Software initiator does not like changes. If you use iqn's for access control on the iSCSI target changes like these are simpler since you don't need to modify the ACL's when changing the initiator ip-addresses provided that works with your iSCSI target of course.
I'm not sure about your first question, I've never paid attention to that message on an ESX console after I've changed an SC address. Two questions -  does the new address work for web management?  Did you re-create\directly modify vswif0 when changing the SC address or did you just add a new SC port and disable vswif0?.