is it possible to modify the rear windows on a 1998 neon so they will roll all the way down?

Sure, if you modify the rear side of the door so it does not follow the contour of the fender. Seriously though, no.

is it possible to modify the rear windows on a 1998 neon so they will roll all the way down?
Take a good hard look where the door meets the body of the car. There is no where for the window to roll into.