1. Antonyms for Alterable include established, fixed, immutable, inelastic, inflexible, invariable, nonmalleable, ramrod, set and unadaptable

2. Adaptable - capable of adapting (of becoming or being made suitable) to a particular situation or use; "to succeed one must be Adaptable"; "the frame was Adaptable to cloth bolts of different widths" unAdaptable - not Adaptable