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All this does is allow you to store different Master Passwords for different accounts.
There is nothing to prevent you from typing a different Master Password in the entry field, and the password will be different for each Master Password you type.
I use a different Master Password for my important accounts (financial, etc), another one for some accounts I manage for other people (one for each), and a simple one for unimportant accounts (like forum/wiki accounts, etc)... all told I probably use 6 or 7 different Master Passwords.