Can I unscrew the T needle valve assembly as 1 unit while mounted on the tank? The reason I ask this is I am not sure if I have a bench vise or not. If there will be a high risk of damage to the tank or regulator I could take it to a friends house instead.
I am not sure what you are referring to; the needle valve is already one unit from what I can see in your (blurry) photograph.
A bench vise is the easiest way to do it. You can probably do it without one, but it will be harder.
How about rotate the regulator to this position:
you can take out the NPT to air hose connector, connect a solenoid to the so call "needle valve", then a real usable needle valve or metering valve to the solenoid.
You can do this too, but I would prefer to remove the needle valve that is currently on there for a cleaner look in the end.