The whole idea behind a double butted is to try as much as possible to have equal length straight gauge between the thinner butted center portion. Because of this, there is an equal tension placed on the straight gauge portion which directly leads to the thinner portion/middle of the spoke to flex as close at/to the center as possible. Can you cut the end of a double butted spoke to fit? Of course you can. Will it work? Yes, of course. Wheels overall are an absolutely wonderful design/work of art. They are built to be terribly strong and are a Physics dream to rotation under torque. But as soon as you start pulling away to much distance from the end of the spoke, you begin to lose your center of relieving stress from the center of the butt. Yes, it will still work, but if you have to cut too much, just save the integrity of the design and get the proper length spoke.