globally change the account password -- possible?

There's no global 'reset all account passwords' feature, as far as I am aware. However, this could be achieved with a spot of scripting if you know what you're doing.

The directory /var/cpanel/users contains a set of files pertaining to user data, each of which is named the same as the account to which it applies - this would get you a list of all cPanel account usernames.

Combine this with a secure wrapper for cPanel that authenticates with the given username and the root password, your script can loop through the list of usernames and change the password for all of them much more quickly.

So yes it's possible and yes it's entirely feasible.