I'm still really new at this and don't fully understand pretty much anything yet...
But, I created a secret room in my level by attaching a "ObjectEventTrigger" (OnHit) to a doodad, so when that doodad is hit, it destroys that doodad and spawns another doodad using "SpawnObject" that instead of being a wall, is the destroyed wall. I know you can do this with stages, but I'm not a good enough artist to create different stages of damage in my custom wall.
There's probably an easier and more direct way of doing this, but this is how I let the player hit a wall and open a passage...I'm pretty sure you could apply this to a trigger_button_wall doodad also, you'd just have to link the ObjectEventTrigger to a ChangeDoodadState I believe.