no, this is not the way to act..
changing perspective, since you've to rejoin the client, you'r best bet is to rename the client itself and join it again..
anyway:
google is your friend "delete a machine account from smbpasswd"
something like
smbpasswd -xm machinename$
should do the trick, but I din't tested it
before doing anything: do you have a good and working backup of that server?