This was for having pre-flavoured IPA or ethanol for adding in small amounts to the infusing herbs, where the aromatic herbs may only be wanted in smaller amounts than would be pracicable for a given amount of changa blend, or may have undesirable smoking characteristics when included as the whole herb.

Frankincense infusion sounds particularly interesting... I'd advise thinning them down considerably before including in changa - they're not usually intended for direct inhalation.