beef up vs modify

beef up and modify both are verbs.

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

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

Other hypernyms of beef up include alter, change.

beef up (verb)	modify (verb)
make strong or stronger	make less severe or harsh or extreme
	add a modifier to a constituent
	cause to change; make different; cause a transformation