Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
immūtātĭo (inm-), ōnis, f. [immuto], a change, exchanging, interchange, substitution of one thing for another in speech: verborum, Cic. Ac. 2, 6, 16: ordinis, id. de Or. 3, 44, 176: si verborum immutationibus utantur, quos appellant τρόπους, id. Brut. 17, 69.