The Collaborative International Dictionary of English v.0.48:

Immute \Im*mute"\ ([i^]m*m[=u]t"), v. t. [L. immutare,
   immutatum; perf. im- in + mutare to change : cf. OF.
   immuter.]
   To change or alter. [Obs.] --J. Salkeld.
   [1913 Webster]