Some things to consider.
Will shorten from the muzzle end. to do so from the breech end is a whole lot more work for no gain; the barrels are not choked so there isn't anything to lose from shortening from the muzzle end. So you will recrown as you're losing that section of barrel.
Are some problems you need be aware of.
1. Many times, the bore is NOT dead center in the barrel once you cut back. A small off center is just unsightly, and even those well off center CAN shoot well, but from previous posts, some can shoot pretty poorly once cut back. Have cut back two of mine (using a lathe to cut and recrown) and while there is a small amount of bore-off-centerness, accuracy hasn't changed.
2. The rifle will shoot a bit slower. How much slower depends on several things, but generally a gun tuned for speed will lose a higher percentage of vel. than one running at lower speeds. basically, it depends on how much co2 is being squirted down the bore with each shot...more gas needs the longer barrel more than the smaller squirts of gas from slower rifles.
3. Rifle will be a bit louder as well. The gas leaving the muzzle will be at a slightly higher pressure, which gives it a bit sharper "crack".