Win NT

NT Installs and reinstalls:

SP3 AND SP4 REQUIRE a reinstall after any changes in the network here is a quote from the Microsoft help document on sp3 at: http://support.microsoft.com/download/support/mslfiles/SP340.TXT and http://support.microsoft.com/download/support/mslfiles/SP3128.TXT and
sp4 says identical stuff at:
http://support.microsoft.com/download/support/mslfiles/SP4128.TXT and http://support.microsoft.com/download/support/mslfiles/NT4SP440.TXT

>If you change or add new software or hardware components to your system after you have installed the Service Pack, you need to install the Service Pack again. This is because the files taken from the  original Windows NT 4.0 disk set may not be the same as the files on the Service Pack disk set. You cannot install new components directly from the Service Pack media (such as a new keyboard or printer driver). You must install new components from the original product media and then reinstall the Service Pack.<