fill up vs modify

fill up and modify both are verbs.

Word	Noun	Adjective	Verb	Adverb
fill up	No	No	Yes	No
modify	No	No	Yes	No

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

Other hypernyms of fill up include alter, change.

fill up (verb)	modify (verb)
make full, also in a metaphorical sense	make less severe or harsh or extreme
become full	add a modifier to a constituent
eat until one is sated	cause to change; make different; cause a transformation
fill or stop up