I've done this many times, sometimes just to do something a little "different" with my tires, other times because I wanted the extra contact area of a 60-series with the look of a whitewall. Here I am just getting started on my '81 Imperial, right after I painted it. You can see the bumper isn't on yet, nor any other trim. Note that I was wearing safety glasses, so I'm sure the whole deal would be OSHA-approved.
You can see a little pile of rubber dust right under the tire. Tires sand surprisingly like wood on a lathe. I start by jacking the rear tires off the ground, at least an inch but not much more to preserve some semblance of a proper driveshaft angle. For some extra safety I'll park it against the bumper of another large car (not hard to find at my house). Let somebody sit in the car and listen to the radio I suppose as an extra measure. Drop in drive and turn up the idle just a bit. On an open (non sure-grip) axle, the torque will keep shifting from side to side as soon as you apply pressure to the tires sidewall. I solve this by wedging something under the opposite tire... Something kinda soft and non-lethal like an old tennis shoe. I've been hit by it... Doesn't hurt much.
If you're starting with white-letters, I use a 36 grit grinder to shave them down flush with the sidewall while the tire spins. (Just as any soccermom in a SUV does with a curb.) Then move on to 80 grit, finish with 120. Dry paper, not wet. If you just want to add lines to an existing whitewall, it's MUCH easier. The white rubber sidewall usually goes in/out past the thin black rubber by at least a 1/2". Just allow a 1/4" black area, then sand away the last 1/4". However, it should be noted that the white strip is usually not a perfect circle, so you are pushing the envelope. You can see where I messed up a little using that method on my '73. It's not hard to fix... a little black paint did the job. Now I would probably use black plasti-dip.