Very simple question: can I change the name of my device without causing trouble to Boinc and or BoincStats.
I always just left the default device name and am now having trouble working out which device is which laptop.

Second question: I just created an account to write this post... But the account I created is just for the forums right? I tried my standard user password and it told me it did not exist. I've been Boincing since 2007... I hope this isn't a problem.

This is the BOINC forum, not SETI.
So yes, you do need to sign up here separately.

Not sure about your other question; I always decide on a computer name myself when I install the OS.
I can't think of a reason why changing it would hurt, as it's not used anywhere.

I have changed a device name and as far as CPDN is concerned it treats it as the same computer, just changes the name but the device id which is a number remains the same.