I'll admit it's been a while since I worked with dragon, so my apologies if I'm off a bit.
If it is the Network Sensor appliance image and not the EMS server, you can just reinstall the Network Sensor without any impact on the system. Nothing should be lost on the sensor itself, as all the data is stored on the EMS. Everything should be pushed back down from the EMS server by redeploying the system. You will probably want to save all the settings from the sensor to reconfigure it to connect back to the EMS server, such as the config channel shared secret and such.
If you have it running on your own OS, you can just change the IP and gateway as normal.
On the EMS server you will need to edit the node to update the new IP, commit the changes, and then redeploy.
Hope that helps,