Question for body nerds

[rydra_wong]

Upper trapezius muscles: can I kill them? how do I get them to shut off, or at least stop trying to do all the work?

I am doing a lot of shoulder exercises to try to get my scapula behaving properly, and yesterday I realized that the multi-day headache was very likely due to my upper traps trying even harder than usual to get in on the action and do the work when they are not needed or wanted to, and thus my neck locking up even tighter than usual.

I will take any suggestions anyone's got on how to get them to disengage while engaging middle/lower traps and rhomboids.