In some cases yes, and some no.
Typically the barrel is longer than it needs to be to efficiently use up the volume of air behind the pellet. I remember an equation from somewhere (I think it was for rimfire ammo though?) that showed optimal barrel length for a given projectile and propellent. The same equation would work for springers. But basically, you want the pellet exiting the barrel at the point where the piston comes to rest.
If I remember right, it was said that that distange was 10 inches or so. But don't quote me on that! hehe
As far as accuracy goes, same thing. It's a crap shoot. If you have a rifle with a choked barrel, then chances are your accuracy will drop off. Unchoked, it may get better... May get worse. In a shorter barrel, the pellet leaves the barrel earlier so that the effects of body movment aren't as amplified. There's also the crown. If the barrel isn't cut square and a crown isn't put on, then air won't vent evenly around the base of the pellet causing a tumble or spiral. Accuracy will also fall off.
Inducing a choke in a brarrel is a difficult thing. You could lap the barrel, but all that really does is open up the bore on the breach end. What I've done (and has worked) was to place the end of the barrel in a JIC Fitting press and squeze it to about 3500 PSI or so, then rotate it a quarter turn and do it again then crown the muzzle. I've actually over choked some Crosman pencil barrels doing this.
Shortening a barrel can also cause hold sensitivity that was otherwise not there before. From my experience with a Crosman Quest, recoil became much sharper and faster. Hold sensitivity went up a bit until I figured out where I had to put my hands as the balance of the rifle changed significantly.
If you had a Crosman, I'd say go for it. But since Gamo doesn't sell replacment parts, I'll leave this one up to you. Hopefully someone with the same rifle as you that has been shortenend will chime in soon!
