Yes, the herbs can strongly influence the trip. Some, like mullein, are added for their pleasantness of smoke rather than their effects; others, like pau d'arco, are purely for the extra little edge they can add.
Caapi with a pinch of pau d'arco is my favorite, but I haven't done much serious changa experimentation. In my opinion, the more caapi the better (up to a certain point, of course), so if you can make 5x or 10x caapi leaf I recommend it. This also leaves more room in the blend for things like mint, mullein and lavender, without decreasing the caapi presence as significantly.