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Synonyms for Alter (same or very similar meaning)

WordNet sense 1 (insert words into texts, often falsifying it thereby):
falsify, interpolate

WordNet sense 2 (cause to change; make different; cause a transformation):
change, modify

WordNet sense 3 (make or become different in some particular way, without permanently losing one's or its former characteristics or essence):

WordNet sense 4 (remove the ovaries of):
castrate, neuter, spay

From the ODE community, based on WordNetadd/edit