You may have figured this out from gibblet's post.

For the Tributeyou do not need a bow press (which means youcan do it yourself)to change the modules for the Tribute and it only takes about 10 minutes tops to do. Even if you go to the shop he can do it while you stand there.

While the Trykon would need to be put in a bow press to do the work. So, unless you have your own press it has to go to the shop. Possibly leave the bow there to get the work done.