Anyone confused by the thread title?

I was at walmart looking in the sporting goods
and it would happen that my eyes
wandered over to the gun cases.I spied a nice
new Remington 870 Express Super Magnum.I had
never seen a 870 that would take 2 3/4,3in,and
3 1/2in. so I asked to see it.It had a 26"
barrel,and I thought if I got it I would change
it out for a 18" or 20".Well apparently not,
as I looked closely I could see that the barrel
and "welded" to the front barrel/magazine
support.

1)Is the barrel attached on all super magnums?
2)Can I buy one with a shorter barrel if they
are?
3)If that gun was a fluke and the rest come off
can I use a regular 870 barrel or do I have
to get a 870 super magnum barrel?

Thanks