either cut off the arm or
do it the right way.
I have removed over 30 of these things over the years. Its easy.
It diverts the extra pressure to the front right tire.
The valve has three lines on it. One is pressure, another is output to the rear hose/tee, the last is a return line going to the front right corner.
If you remove the valve you need to unhook the two lines going back up front (pressure and return). Now go up front and find the right front brake hose, follow it up to the framerail and it will go to a tee under the fenderwell on the framerail. There is only two fitting on the frame right there, a elbow and a tee, the tee is the one you want.
Once you have found the tee, leave the line going down to the hose, leave the line going up to the master, UNHOOK the line going to the rear of the truck. Go to the parts store and get a plug to plug the hole in the tee or replace it with an elbow from a parts truck.
Now take the loose line up front and blow thru it with your mouth or compressor until it spews out fluid and air from one of the loose rear lines. Whatever line is blowing in the rear is marked and bent out of the way. Dont kink it as it can be used as a spare rear line if you ever need one on the trail.
Now hook your rear brake hose to the remaining line that was NOT blown out.
Now the valve is completely eliminated and you have an extra rear hardline already installed from front to rear if needed.