when adding the custom trigger to the rule(s), do I simply add it below my existing triggers for each of the merchandising rule(s)? 
no, like i said, the custom trigger is a replacement for the other triggers, not in addition to.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.