Custom code in selected topics

[Damer]

Hi!
I was wondering if there was a way to add custom javascript to individual threads in vB5. We have a community board where we do "quests", complete certain tasks on a weekly basis. We were wondering if we could add a bit of extra gamification, like:

a) a countdown to every quest's thread
b) confetti - when we complete a quest: http://codepen.io/iprodev/full/azpWBr

Is there some way this can be added to selected threads? Users don't need to have this function, we can add it every time - I am just not sure how to do it or even where to start, vB5 is so complex. When you modify vB5 template it changes every page of this kind and we need to add it just to the quest threads.

Does anyone know how to do it? Thank you so much in advance.