Mutability and immutability, from the Latin mutare ( ‘to change’), are both modal terms; the one means ‘possible to change’ and the other, its negation, means ‘impossible to change’. Change refers to any passage from potency to act (cf., Al-Shifa’; Tabi’iyyat, II.1.2.108). As such, change necessarily requires two principles, i.e., matter and form; and one condition, i.e., privation (cf., ibid., I.2.12.18). The Peripatetics all agree on this.
Grant then, without argument, that certain substances (i.e., what religions call ‘angels’) are separate from matter and its concomitant privation. From this, it follows that immutability is not an exclusively divine attribute. The claim that such beings have potency, and hence (accidentally) change, with respect to their choice (cf., ST.I.9.2) is dialectical (at best). And the claim that such beings act in distinct places (cf., ibid) no more entails (accidental) change in them than it does in the case of God, despite the fact that He too acts in diverse places, i.e., insofar as, according to the adherents of the contra position themselves, at whatever place the rational soul comes into existence, at that place God directly creates it.