After turning off the gas and unplugging the electricity, I removed all the burners from the stove top using a 3/16" hex socket. Then used a 1/4" socket to removed two or three screws under each burner which hold the burner base to the bottom of the top panel. Then pulled all the knobs and removed the front panel which was held in by two Phillips screws accessible from underneath the panel. It helps to open the oven door to get at these screws. With the knob panel gone, I removed two screws holding the stove top panel, pushed all the burner bases down slightly below the top panel, slid the top panel out to the front about 1 inch to clear some tabs, and lifted it up off the frame. All the valves and gas piping were now accessible.
I gently pried the plastic igniter switch loose from the broken valve, but did not remove it completely. Next unscrewed the bolt holding the valve to the gas manifold using a larger hex socket. The valve dropped out easily and was pulled free from the igniter switch.
The replacement valve came with gasket washer installed and a new bolt (with it's own washer installed). So it was very easy to reverse the process and put it back together. In summary: Slide the new valve stem over the igniter switch while installing from the below the gas manifold. Bolt it in with moderate force. Press the igniter switch tightly to the valve. Connect the burner gas line while making sure the burner base is oriented correctly and looks like the other burners. Put the top panel on and secure with two screws at the front, then guide the burner bases to the holes and screw them in with mild torque. Screw the burners on with light torque. Note that I used a tiny amount of anti-seizing compound on these small threads. Don't know if that is recommended, but it was intuitive to me. Screw the knob panel on and push the knobs on. Note: There were two different size knob shafts on my stove top. It was obvious knob which went to which valve.
BTW, my stove top had four different size burners, each with a different valve part number. Carefully check the mechanical drawings for your exact stove top and order the correct valve.
The job took about 35 minutes but I was in no hurry, and didn't want to break anything getting it apart. It required only 4 standard tools - #2 Phillips, adjustable wrench (for gas line nut) and 2 small hex sockets with a 1/4 inch drive. Overall it was an easy task for a DYI'r. Having done it once, the next time should only take me 20 minutes.