recognise and match an IP address with a user name and then send an automated response when another name was entered, asking if a name change was required.

I guess the only problem here would be if multiple users were logging in via a single school's/office's network. The IP address may be the same but the users would presumably be using different names and in this case are genuinely different people. Such cases may be the exception rather than the rule yet going back to your initial point about Murphy's law ................