I use the following steps on the master machine to clone an AIX system:
1) Remove the password from root.
2) Remove the NIS line from the end of the /etc/group file (the last
   line with the +: )
3) Change most of the level '2' designations in /etc/inittab to level
   '3' to prevent them from being started up when the new system is
   booted (the minimum ones to change are rc.nfs and rc.tcpip)
4) Boot in service mode and change the name and ip address to a "spare"
   set to avoid address collision.
5) Clear /tmp, /usr/tmp and /usr/spool/lpd/stat.
6) Run mkszfile and edit it to be sure /usr is as small as possible;
   then mksysb from the command line.

The above changes allow me to boot in normal mode the first time, get in
as root, change the above files back and do the other things necessary
to configure the new system.

Then, of course, I go back and clean up and reboot my master machine.

Note: 1 and 2 lets you log in even if you can't get on the network. 
   It prevents the login process from trying to reach an NIS server. 
   Step 2 needed only if you use NIS.

Some parts © 2009 Advameg, Inc.