When poking the xacto knife in, just do it slowly, and angle the blade inwards towards the plug. I do lots of tiny stabs instead of slicing. I also grasp the neck plug by the little notch, with pliers, and tug at it. I rip it out of there as soon as it will come out. Sticking the neck in hot water for a bit helps too
And yes, the only way to get white is to paint.
If you paint the head white, I would suggest putting at least a thin coat of white on the body too, just so that the texture and white match.