Generally, I think there are three ways to make an object/NPC respond to you:

* Right-click (also left-click if you have the option configured, I think)
* Target it and then type /interact (this might be obsolete or something)
* Target it and press the key you bound to IWT in Blizzard's keybind options

From a technical standpoint, /assist is not an action as it doesn't affect anything in the game world. We've been using /assist or /target and variations of those since multiboxing began. It is, along with /follow, the core of making multiboxing actually work in WoW. Everything is built on /assist'ing the right person to target the correct object and then taking action on it. Nothing new, there.

A longer answer would be that what Blizzard is concerned about (for now) is automation. As long as your character requires you to press a button anytime you want it to do something, and it stops "doing stuff" when you stop pressing buttons, you're fine. The way it was put a while back was, consider if you have a popsicle stick across keys 1-6. If you press the popsicle stick once, it presses 6 buttons, but you're still only able to perform the actions that Blizzard's client allows to happen within that Global Cool-Down. Ergo, why they have the GCD. So, the client prevents you (as long as it only takes action when you are pressing or releasing a key) from doing things Blizzard doesn't want you to do, broadly speaking.

That said, I can't count the number of people I've heard talk about using one of the programmable keyboards or gamepads that presses a bunch of keys in sequence as long as you are holding down a button, which technically violates their policies, but I've never heard of anyone getting banned for doing it.

Short version is: don't be a dick or a cheater* and they pretty much won't care about your multiboxing. (* = ignore what the battle.net forum warriors think "cheating" is)