Your description suggests that Brand X rotors were installed, a lower
than OEM quality rotor. That's why they warp.
Turning the rotors a second time will reduce their useful lives, as you
point out, but you're already in bed with them, so to speak.
IMHO, if the shudder occurs after a second grinding the rotors ought to
be replaced - they're just lousy rotors.
Good, OEM quality rotors ARE available.