When I did a 7.3->7.3 upgrade using kickstart, I got No kernel packages were installed on your system. Your boot loader configuration will not be changed when no kernel was updated. I had to press return to finish.
This is very likely to mean that your bootloader could not work after upgrading, so there's no way I'm going to make this silent. If you use 'bootloader --upgrade', you should avoid ever getting the warning, though.