I didn't know that you could have a trap trigger a spell.
In D&D you could easily -- but in Conan? Dunno -- not very Conanesque.
Certain items could cause curses like the one recieved but it would be an inherent property of an item and not something that could be subject to a Disable Devices.
Of course, you're new to the Conan RPG and quite possibly the world of Howard. A tip for you and your GM: This isn't a D&D sourcebook. The touch and feel of everything is rather alien to what other fantasy RPGs put forth. Here's how I see the turning of a person into a werehyena going down in a Howard story:
Power Corrupts: the person affected would surely want to take advantage of any control that he could gain over his condition. He is no longer a mere mortal but ferocious beast that can terrorize the country side and looks down upon all humans as weak and insignificant. A new predator lurks in the shadows of Numalia, set up a fiefdom, control his slaves by fear, The Cult of the Hyena, human sacrifice!
By no means would he want to rid him self of the powers gained -- his entire outlook on life has changed now -- the servitors of Zem have turned their feckless gaze upon his tired form and blessed him with unspeakable powers!
Of course he would hide these desires until the time is ripe!
His Companions would be terrified and repulsed by the transformation. Magic is a dark art and they would surely shun the person affected -- even try to kill him. Those with a code of honor would do so to put the poor fellow out of his misery, those without because he's a threat to their lives. Companions who have gained some corruption might forego violence and instead try to control or befriend the beast, gaining his might and favor!
Whenever I run into a problem like yours I try to ask myself: What would Conan do? There's no doubt in my mind that he would either flee or kill the werehyena. There would be no quest, there would be no desire to tolerate him -- at best there would be only pity that a life was thus lost.
/my 2 cents