What would the symbol look like, and how would it sound like? E.g. a long rhotacized nasalized vowel with tone?
The IPA doesn't set a limit. For example, an overlong breathy nasalized creaky high-tone rhotacized mid central vowel would be
However, the symbols quickly become unwieldy when you're applying too many diacritics. Look at "Zalgo text" for an extreme example. So most if not all linguists would pull off at least one of these diacritics, e.g. by using a tone letter instead of the acute accent: