renaming the system users bin and man without doing harm?

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http://unix.stackexchange.com – In my setup I need to rename the linux system users man and bin because I need the usernames for humans. I am using Ubuntu 12.04. I know that I have to change /etc/passwd, /etc/shadow etc., but when updating through apt, packages use the man user for their man pages, and those files would have false ownership then. Is there an configuration option in Ubuntu where I can set how the manual user is called? Same with the bin user: I don't know when it is used but I assume changing its name will mess something up. Thanks in advance! (HowTos)