Well, if it can fire LIVE REAL BALL ammo, it is not a blank gun, And the Feds are a tad fussy about that, since there is a Federal Excise tax paid by the maker of real guns, but not blank guns.
To answer, a blank pistol will GENERALLY not be built to the same standards of construction of a real gun- weaker metals, etc. So it is not just replacing one part.
There were some STARTER pistols (think of the start of a track meet) that looked like a regular 22 revolver- but with a very short cylinder, and the barrel was a solid chunk of steel- with a point right above the face of the cylinder. Actually made report louder, and no way to fire a ball round, except replacing the cylinder AND barrel.
IF you replace all the parts, you have rebuilt the gun, spent 4 times what it would cost, and still have a Frankengun that is liable to hurt you. Even 22 LR has some decent pressures.
There used to be a company back in the 60's (may still be around) that made and sold very realistic replicas- even stripped down like real thing- but to get their 1911A1 to shoot, you would replace the barrel, slide, provide a firing pin, firing pin spring, extractor, ejector- and THEN find out that the slide dimensions did not match up. And still have a pot metal frame that would crack at the first shot.
Run a google search for zip gun. And if you do this, please do not attempt to shoot in the area of innocent bystanders.