i know what you're trying to do, but i dont think its possible.
the only thing you can do is (if you're not running an hotel) is to call the hashed function (revcms) and ENTER the password you want for e.g.
http://puu.sh/n9oRl/38e94346ae.png
note the bit i've highlighted, i just outputted a password that i want, then copy what it gives off and then manually update your pass through phpmyadmin
IF you're running an hotel, i guess the only thing would be to set all users passwords to 'default' or something and then make a changepassword page after they've logged in