RonNNN wrote on Wed, 7 Dec 2016 06:35:52 -0600:

> Yes. And as you've posted the video's you now know you can change the
> stem without removing the tire.

Thanks for confirming that the cheap tool works just fine for my purpose,
where the tire is already off the rim.

The one hook-and-funnel tool works with the tire on the rim, whereas the
rest of the tools I found work with the bead broken at least well enough to
get your hand in there.

Since I've seen in the videos people replacing the valve by breaking the
bead while the tire is still on the car, one guy had a neat trick where he
tied a long string to a drywall screw and before he cut the old valve stem
in half, he screwed the screw into the backside (inside the tire) of the
rubber valve stem.

That way, if the inside cut-off rubber part fell, he could retrieve it
easily. For him, this was important because he was breaking the bead with
the wheel still mounted to the vehicle.

For me, the tire will always be off the rim so I don't need that
string-and-screw trick, but it's nice to know about in a pinch.