How To - Change which port numbers are associated to port names

In some cases (not many, but some) you may wish to change the port numbers associated to various port names.
 
For example, RADIUS Authentication has a confusing issue with port numbers where some servers default to 1645 and other default to 1812.
 
Changing these values as outlined below can have wide ranging effects on applications running on the machine and could cause problems that appear unexplainable during many support calls - be careful here.
 
Under Windows NT, there is a SERVICES file located in the %SystemRoot%\System32\Drivers\Etc directory which contains these port name to port value associations.  IPSentry makes use of these settings when converting a port (service) name to number (such as SMTP to 25).