In this variation of the standard rules, characters may activate reflexive charms during the course of performing a Shape Sorcery action.
This rule has two key effects – first and least important, it allows sorcerers to use their excellencies (and other charms) to help them maintain concentration when casting spells, and second and most important, it allows them to use their charms to protect themselves from attacks while casting.
Characters are already allowed to parry and dodge while casting, so there’s no particularly logical simulationist reason why they shouldn’t be able to defend themselves with reflexive magic as well. Moreover, without magical defenses, a spell caster drops into an entirely different and inferior tier of combatant, making combat sorcery a practical non-starter.
Though there are any number of powerful and useful spells, there are few or none which offer outcomes that simply must be stopped, and as such the standard rules put casters at more risk than the outcomes they can achieve merit – over and above the high cost of the spells themselves.