Quoted:
Short answer no.  Long answer yes, but.

The ATF says no but then again who would find out before next year?  Youd have to do something pretty bad to catch that much scrutiny.

THere are ways to do it but the stock must not be convertabel back to collapsing form.  It essentially must be impossible to turn back into a collapsing stock.

Quoted:
Thus making it 31" overall, the legal limit is 30" correct? I remember having to measure the Mossberg to make sure....

USC 18 Sec. 921:

(5) The term ''shotgun'' means a weapon designed or redesigned,

   made or remade, and intended to be fired from the shoulder and

   designed or redesigned and made or remade to use the energy of an

   explosive to fire through a smooth bore either a number of ball

   shot or a single projectile for each single pull of the trigger.

     (6) The term ''short-barreled shotgun'' means a shotgun having

   one or more barrels less than eighteen inches in length and any

   weapon made from a shotgun (whether by alteration, modification or

   otherwise) if such a weapon as modified has an overall length of

   less than twenty-six inches.

     (7) The term ''rifle'' means a weapon designed or redesigned,

   made or remade, and intended to be fired from the shoulder and

   designed or redesigned and made or remade to use the energy of an

   explosive to fire only a single projectile through a rifled bore

   for each single pull of the trigger.

     (8) The term ''short-barreled rifle'' means a rifle having one or

   more barrels less than sixteen inches in length and any weapon made

   from a rifle (whether by alteration, modification, or otherwise) if

   such weapon, as modified, has an overall length of less than

   twenty-six inches.

Quoted:
If you weld it in place its totally legal.

The question is do you want to ruin it like that when it may be legal in 11 or so months?