Hey Sim32,
Hicas is only like a 1 degree turn in the rear wheels and only kicks in at 80km/h and above (some say it works at all speeds)...correct me if i'm wrong. It will make that car feel somewhat floaty in the rear end. It's suppose to help overall handling of the car, but most people will agree that it's not that great at all. Yes you can lower the rear without doing anything to the hicas. You can get hicas locking kits that disable it.....and i'm not sure what will happen if you pull out the fuse....maybe do a search.
Here are some other threads that might be helpful:
http://www.skylinesaustralia.com/forums/sh...=&threadid=8292
http://www.skylinesaustralia.com/forums/sh...=&threadid=8970
http://www.skylinesaustralia.com/forums/sh...=&threadid=9188
Scott.