Usage of "I couldn't agree/disagree more"

Solution 1:

• So, by altering the phrase in question, does this become wrongful use of language because it is no longer in the form native speakers instantly recognize?*

No, it doesn’t make it wrong. It’s a way to attract attention to the phrase. It might take some time for the reader or listener to figure it out, and thus may be distracting or misleading. If the writer is not fluent, it may be seen as awkwardness rather than intentional varying of a common phrase.

Solution 2:

The problem with 'I couldn't agree any less' is that one may be left wondering: less than what? It could be 'less than I, in fact, agree', which makes the sentence an expression of disagreement. It is possible, however for the sentence to be an expression of agreement: in a context in which somebody has already expressed agreement with something, one could use the sentence intending it to mean 'The reasons for this are so compelling that I couldn't agree with it any less than this other person agrees with it'.

Now, in the abstract, 'I couldn't disagree more' could also be said to give rise to ambiguities: more than what? That wording is, however, much more frequently used as an expression of strong disagreement than 'I couldn't agree any less', so, in practice, people are likely to immediately 'get' what was intended by it. In 'I couldn't agree any less', because it is rarely used, one is more likely to 'hear' the ambiguity; even if the ambiguity is easy to resolve in a particular case, it will add a second or two to one's processing the meaning of the sentence in one's mind.