>>> resources for this virtual machine can only be done from <Ip_address of vcentre server you just shut down>....
The steps you mentioned are basically correct. Add another virtual disk with the new controller type to force the guest OS to load the drivers. Then shut down the guest and modify the settings by connecting the vSphere Client directly to the host. With the above mentioned message, I'd assume you enabled "Lock Down Mode" for the host, which - in this case - has to be disabled prior to shutting down the vCenter Server.
André