alteration has 4 distinct synonyms spread across 3 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
an event that occurs when something passes from one state or phase to another
“the change was intended to increase sales”
the act of making something different (as e.g. the size of a garment)
the act of revising or altering (involving reconsideration and modification)
“it would require a drastic revision of his opinion”
Synonyms, antonyms and the broader and narrower relations for alteration come from Princeton University’s WordNet. Full sources and licences.