fixing vs altering

fixing and altering both are nouns.

Word	Noun	Adjective	Verb	Adverb
fixing	Yes	No	No	No
altering	Yes	No	No	No

As nouns, fixing and altering are synonyms defined as:

Other synonyms of fixing include neutering.

fixing (noun)	altering (noun)
the act of putting something in working order again	the sterilization of an animal
the sterilization of an animal
(histology) the preservation and hardening of a tissue sample to retain as nearly as possible the same relations they had in the living body
restraint that attaches to something or holds something in place