Can the ball be snapped from a spot exactly ON goalline?

[Barcelona]

I mean a situation, where the most forward point is in the field, but the rear part of the ball is on or behind goalline.

Possible scenarios, how to achieve that could be as follows:
-punt/interception is caught deep in the endzone, runner tries to run out, but is tackled so, that most forward point of the ball is at "on-inch-line", but rest of the ball is in the endzone (touch what matters? That most forward point and R´s ball from 1-in or is it a touchback?)
-Team A snaps from very close to own endzone and commits (multiple) penalty, which means half the distance. But what distance is halved? Goalline to most forward point of the ball (what would move the rear part of the ball on the goalline) - or - goalline to the "end" of the ball?
-Team A on fourth and goal is stopped inch(es) short. From what spot will Team B snap the ball? Exactly where left by Team A (because of turnover, the most forward point will move one foot closer to Team A´s and zone) or is the ball turned around the most forward point (and part of the ball will be placed on the goalline)?

Thank you for help