Is there any way to make a std RWS 34 into a switch barrel so I can try other calibers (20 and 22) in my rifle?

Thanks, Andy

You could get a .22 barrel and swap it. The .177 spring may need cutting down as the .22 needs less spring power. You don't want the piston wacking the end too hard.

If .177 ain't doing it for you, change it or swap it. The main reason for .177 is in lower power guns for flatter trajectory.
But at 45 yards or less it should kill anything you'd hunt with an airgun. You do need to hit the heart or brain with a .177, a .22 will give a bit more leeway.