[Jim S]

Sorry guys, I have to study for a licensing test tomorrow so I don't have time to find when the rule changed in the old books this time.
But, the old Fed rule did prevent the snapper from lifting the ball to adjust it. A smart defensive player would then reach across and tap the snapper. ( A dumb one would blow him up getting a 15 yarder).
The rule was changed somewhere around 15 years ago to alow the snapper to pick the ball off the ground to do his adjustment. You'll notice that most snapper now make their adjustments before the line becomes set. Several good reasons for this.
We, as umpires, used to be religious about setting the ball down with the laces just so. The 'new' rule eliminated the real need to do that. Defenders should be taught that the adjustment is not a live ball.
As far as snappers moving the LOS with their adjustment, it happens all the time. If it makes a difference, such as pushing the ball over the goalline, or past the LOG, either I as an umpire, if I can tell, or the sideguys should jump in with the old preventative, "Get a dry ball" (or someother such ploy to hold up the play and admonish the snapper.