Basic answer is yes, you can change barrels, gas tubes, and handguards to get the length you want.
The length of the barrel doesn't determine accuracy though. at 300 yds and shorter distances a match quality 16" barrel would still get you the accuracy that you need. The extra length gets you more velocity which can give you a flatter trajectory, but that is not the smae thing. The only other advantage that you get is a longer sight radius if you are using iron sights, but if you use a scope, then that advantage goes away.
If you took a match barrel at 20 inches and cut it back it would actually have more accuracy potential by virtue of the fact that it gets more rigid.
So, the criteria to look at for your next barrel are:
- Who makes an accurate barrel?
-What kind of velocity do I need to have the desired effect at the intended range?
-Am I going to use optics or iron sights?
Otherwise you may have more weight and length than you really want, and reduce the handiness of the rifle.
Just some thoughts.