I have a similar question.
I just set up my new box which came with Yosemite pre-installed, and so it's linked to my iTunes account.
When I boot the computer I need to type in my iTunes password and when it wakes from sleep, but I'd rather use a different password than my iTunes password.
If I changed the password for my login will that change the password for my iTunes password as well? I just want to change the login password and keep my iTunes password as it is.