I have not used the Dahua Config Tool so I can't answer those questions.
My cameras are on a different subnet too. After doing a reset via the web interface, I then took my laptop,turned off it's wireless, and plugged it's ethernet into the camera's subnet ethernet switch. I set the IP...
I did the factory default via software before updating. I didn't do it again after, never thought of that, but have not had any problems. I never touched the actual camera.