This tutorial at the bottom shows you how to change the Text for the Logon screen for Windows 7.
In addition to clicking through all the windows to get to the Local Security Policies interface, you could simply typed in secpol.msc in the search box.
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To edit the part "Login to Ratology in Windows 7", you have to click on "Interactive logon: Message title for users attempting to log on."
- To edit the part "To log in to Ratology domain: enter "Ratology\" prior to your user name.", you have to click on "Interactive logon: Message text for users attempting to log on."