The 2nd edition core book, on pp. 251-252, seems to make it clear that reflexive supplemental charms can't be used while shaping sorcery or while casting a spell.
This hugely reduces the value of the Occult Excellencies, including the Abyssals' Ravening Maw of Occult. While there are things that those charms can be used for, their value is greatly reduced (and indeed other than spellcasting I can't think of a use for Ravening Maw of Occult).
So, first, am I reading the rules correctly? Second, are there ways around this? Third, realizing how subtle and far-reaching the Exalted rules balance tends to be, are there inobvious second-order effects that would arise if I allowed a PC to use Occult Excellencies in support of sorcery and necromancy actions?