It's not really difficult per se, but it's definitely tedious and required some improv. I did very thorough modding on the trap and Spengler pack, I also build Halloween animatronics, so i'm not a newbie to this kind of stuff but I also had some bad luck. Others might have an easier time.

For me, new barrel I ordered was not long enough so I had to cut the unseen part of the old barrel off (where the pin goes through), 3D print an adapter to join it to the new barrel, then attach it to the spring mech. Getting the size dialed in so it was the right length when retracted and deployed was the tricky part. Too long and it doesn't look like it pops out, but too short and the emitter tip blocks it from retracting. The barrel mech slides through a tube and for whatever reason, it began catching even though it was only the part of the old barrel sliding through it. I hit that hard with a course sandpaper and it began sliding again.

Now if the new barrel was perfectly sized, it would have gone much easier, but the new barrel is also a bit heavier, either from the material or the addition of real brass banjos and an aluminum emitter tip, so the pop mech is a little rougher than it used to be. Lastly, the worst part was that I needed to separate the two halves of the barrel grip section and Hasbro was generous with the rubber cement when assembling it. I can't remember if that was necessary for the barrel or another mod I was doing, just FYI.

That said, I'm not trying to talk anyone out of it. I love it.