You can use the host/ option to do a rejoin as long as the computer object already exists and the host.keytab exists in the etc/opt/quest/vas directory.
vastool -u host/ join -f -n<hostname></hostname><domain></domain>
This will work, but it will give an error: Joining computer to the domain as host/<hostname></hostname><domain></domain>... Failed
The error appears because you are re-joining using the host/ credentials and it does not have rights to modify its own attributes (unless you put that computer object in the Administrators group).
It will modify the hosts password attribute which is all that is needed to do a rejoin.
You may ignore the error.