The Collaborative International Dictionary of English v.0.48:
Mutableness \Mu"ta*ble*ness\, n. The quality of being mutable. [1913 Webster]WordNet (r) 3.0 (2006):
mutableness n 1: the quality of being capable of mutation [syn: mutability, mutableness] [ant: fixity, immutability, immutableness]