impact vs modify

impact is a noun but modify is not a noun.

Word	Noun	Adjective	Verb	Adverb
impact	Yes	No	Yes	No
modify	No	No	Yes	No

As verbs, modify is a hypernym of impact; that is, modify is a word with a broader meaning than impact:

Other hypernyms of impact include alter, change.

impact (noun)	modify (noun)
influencing strongly
the violent interaction of individuals or groups entering into combat
the striking of one body against another
a forceful consequence; a strong effect

impact (verb)	modify (verb)
have an effect upon	make less severe or harsh or extreme
press or wedge together; pack together	add a modifier to a constituent
	cause to change; make different; cause a transformation