This is not officially supported, but I just tried it on my lab box and it seemed to work fine.
Edit the registry key HKLM/Software/Cisco/CiscoAAAv3.x/CSAdmin/HTTP Params/Port, you'll see it's currently set to 2002. Change it to whatever you want (not in the range 2000-2010, nor 1645-1646 or 1812-1813). Restart the CSAdmin service under Control Panel and you should then be able to connect using the new port.