are there any IOS commands that can be used to stop/kill/halt IOS image transfer via TFTP ?
If you are telneting to that device via the port you are planning to shut down, you need to be careful thus I understand your concern :)
If the key combination isn't working as suggested, you can apply an ACL to the interface facing the TFTP server.
ip access-list extended KILL-TFTP
deny udp any eq 69 any
permit ip any any
ip access-group KILL-TFTP in