Leave the machine plugged in. Only the displays and Power Supply have HV with the machine is on. Leaving the machine plugged in provides a ground that you should use with a ground wrist strap attached when handling the boards.

In reality if you have the machine plugged in, and are touching the glass top metal rails you are
grounded preventing a static discharge that would damage your boards. You are more of a problem, than any dangerous voltages when the machine is turned off.

The power supply has the HV. The only time you have to be concerned is with the machine is on, and you are working near the PS HV or displays - primarily when measuring the HV.

With the machine off, your only HV concern is with the AC coming into the machine at the RF filter and power switch if there are exposed connections.

I shock myself damn near EVERY TIME removing the sys 3-6 power board.

The caps hold up a high voltage for even 10+ minutes it seams. When i go to thumb wheel off the power board top left pin (yes i use thumb screws in my test bed) i always hit one of the + or - 100v pins on accident with a finger. No more than a jolt that makes me jump.. but damn i always do it. Nothing is going to hurt you....

Worst i have felt is a leaning my arm into a bally rectifier board being hit by 230v. Its not going to kill you, but unpleasant.

To add to barakandl, the shock doesn't hurt you as much as your reaction when you pull your body part away and run into something sharp and hurtful.