Sorry Vonkas, but in fact this is a TREMENDOUS POWER the OSX gives you. Try to imagine a computer at company X that has just hire a new worker to replace one that just left the company, obviously the new user would like to continue all pending work from previous user but having everything with his own name (i.e.: home folder ;-) ).
Just logout from any account and then logging using the previously enabled "root" account ... with the Netinfo Manager tool you can easily achieve all needed changes. REMEMBER netinfo is the local DB for all you users, groups and a few more things so be aware that improper settings might render your OSX unusable ... in that case just boot in single user mode, mount the root partition and delete the /var/db/netinfodb/ directory and your machine will, after a convenient reboot, go through all the configuration screens as if you just installed new system.
Just in case you all want more detailed howtos .. just let me know :-)