CC, you might want to check a few of these "facts" with the CFC.
The OAL does not matter as long as the gun was not cut, folded, collapsed or otherwise altered to get to that length (read the definitions of restricted and prohibited on the CFC website). If you can bolt together unaltered "factory" components and the result is less than 26" it is still NR, ie Ranch Hands. They don't consider changing "factory" barrels to be altering these guns.
Your example one had to be over 26" because you shortened the buttstock, if you had a "factory" short lop buttstock and the gun was under 26", OAL wouldn't matter, ie Mare's Legs
No barrels are restricted on these guns (other than a couple of bizarre prohibs because of caliber), only the frames thus if you put a short "factory" barrel on your NR carbine and it came out under 26" OAL it would still be NR as long as it didn't get that way from cutting, folding,collapsing or altering (you can adjust lop a reasonable amount and still be within the law) You could shorten a pistol barrel but then the gun must be over 26" OAL as it got that way by cutting the barrel. If you got a really short barrel made by MGM or Brown and put it on then the OAL would not matter.