Which messages are you talking about ?
I can only advise you some parts from Oracle Documentation:
For Active Directory and LDAP directories, there are enhancements to how SGD handles password expiry. SGD can now be configured to do the following: Display a warning message on the webtop, telling the user that their password is about to expire
Deny authentication and force the user to reset their password at the next log in.
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If you have any questions, ask.
If the message is pretty static (and it reads like it is), you could edit the JSP and add your content. For the standard webtop, the page is: