Here is some code that may help you out. It is used to change the address of a mindsensor sensor, don't know if it will work on a hitechnic sensor, I think it will, excluding the sensors that come in the nxt kit.
all you need to do to use it is to change the last line of code and set the port of the sensor.
Change_add(Current Address , New Address);
This will change the sensors address from 0x02 to 0xA2
After that I suggest using this program to scan the port to make sure the address got changed. Make sure you sect the correct port to scan in the code.
Good luck, hope this will help B-)