In most grammars, an adjunct is differentiated from a complement in that the former modifies something whereas the latter complements something. But is it really the case that what an adjunct does is modify something?
For example, here are a couple of sentences from CGEL (page 222):
 i She treated us remarkably well. [obligatory: complement]
ii She carried out all the duties remarkably well. [optional: adjunct]
Here, the adverb phrase (AdvP) remarkably well is a complement of treated us in [i] and an adjunct of carried out all the duties in [ii]. But does the AdvP in [ii] really modify carried out all the duties in any way, shape or form? All it does is simply describe the manner in which she carried out all the duties. It doesn't modify even slightly the fact that she carried out all the duties.
In fact, modify something is what the AdvP in [i] does to treated us, the meaning of which would be different without the AdvP in [i]. Therefore, I believe that the terms modify/modifier/modification should not be used to describe the function of an adjunct, because these terms actually describe the very function of a complement such as the AdvP in [i].
So, I was wondering why grammarians would even use these terms modify/modifier/modification when they describe the function of an adjunct. Am I missing something here?
Thanks to StoneyB's comments, I've gotten to know that the word 'modify' used to mean 'limit, restrict' when first adopted as a grammar term, and that that meaning has been mostly bleached over time. Since 'modify' mainly means 'change or alter' in the present-day English, I think it'll inevitably lead to confusion when the same term is used in grammar not as 'change or alter,' which describes what complements do in grammar, but as 'limit, restrict', which describes what adjuncts do in grammar.
Considering this confusion, why not abandon the term 'modify' altogether as a grammar term? Or am I the only one who thinks this is unnecessarily confusing?