When connecting my pc to android wifi hotspot, It assigned a 192.168.42.x address to my pc. I really need to change this as it conflicts with one of our work subnets - is this possible?
Unfortunately, there is no way to change the IP address range for the builtin tethering support, even in CyanogenMod. The Wi-Fi hotspot IP is hardcoded in android.net.wifi.WifiStateMachine.startTethering(); the USB tethering IP is hardcoded in com.android.server.connectivity.Tethering.
However, if your phone is rooted, you can try using third-party apps for tethering which have the option to change the IP address range. E.g., when the builtin USB tethering was broken in CyanogenMod alphas for Samsung Galaxy W, I used Wired Tether for Root Users, which has such option. For Wi-Fi tethering you can try the Wireless Tether for Root Users app from the same authors, which also has the option to change the IP address range.