I've recently done this on my 1984 Fuji, probably original pads. These are studded holders so I did not have threads to protect. Clamped the holder in the vice, stud between the jaws, and rolled the old rubber out grabbing it with "channellock" pliers. I then warmed the new "weinnman X" pads in hot soapy water and rolled them in. For assurance I then unclamped the stud, slid it down into a long socket from my socket set and put that back in the vice. Squeezed the whole thing a bit to ensure the new pads were seated in the holder.
On another project with threaded four sided holders, I broke off one of the end tabs and slid the new Koop stops in. I'm clever enough to orient the holders correctly when I install them on the bike. I do paint the open end silver in case I'm spotted by a CPSC officer. No hard time for violating Federal regs.