modification vs occurrence

modification and occurrence both are nouns.

Word	Noun	Adjective	Verb	Adverb
modification	Yes	No	No	No
occurrence	Yes	No	No	No

As nouns, occurrence is a hypernym of modification; that is, occurrence is a word with a broader meaning than modification:

modification: an event that occurs when something passes from one state or phase to another
occurrence: an event that happens

Other hypernyms of modification include happening, natural event, occurrent.

modification (noun)	occurrence (noun)
the act of making something different (as e.g. the size of a garment)	an event that happens
slightly modified copy; not an exact copy	an instance of something occurring
an event that occurs when something passes from one state or phase to another
the grammatical relation that exists when a word qualifies the meaning of the phrase