Does the Master Chymist Advanced Mutagen:
Growth Mutagen (Su): When the chymist assumes her mutagenic form, she increases one size category, as if under the effects of an enlarge person spell. The character must have an effective alchemist level (alchemist level plus chymist level) of at least 16 and must know the enlarge person, giant form I, or polymorph extract to select this ability.
Work on a creature that already has Enlarge made permanent?
It is the words 'as if' that has thrown me off