tone down vs alter

tone down and alter both are verbs.

Word	Noun	Adjective	Verb	Adverb
tone down	No	No	Yes	No
alter	No	No	Yes	No

As verbs, alter is a hypernym of tone down; that is, alter is a word with a broader meaning than tone down:

Other hypernyms of tone down include change, modify.

tone down (verb)	alter (verb)
make less strong or intense; soften	remove the ovaries of
deaden (a sound or noise), especially by wrapping	become different in some particular way, without permanently losing one's or its former characteristics or essence
	cause to change; make different; cause a transformation
	insert words into texts, often falsifying it thereby
	make an alteration to