externalise vs modify

externalise and modify both are verbs.

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

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

Other hypernyms of externalise include alter, change.

externalise (verb)	modify (verb)
make external or objective, or give reality to	make less severe or harsh or extreme
regard as objective	add a modifier to a constituent
	cause to change; make different; cause a transformation