Literally anyone with database access on any social media site can do that to anyone at any time (and potentially even hide it from the person that they did it to) It is why generative AI is being used to create posts on facebook that read like ads for products

…the obvious flaw that said investigations would clearly conclude the posts were doctored?

The metadata of posts include too many data points (IP address, GPS coords, etc.) needing precise alteration in line with the exact movements of a victim that it would just be too complex to achieve a desirable outcome for Musk. Even if the SS’s investigations were subjective in their approach and/or conclusion, independent investigations would provide a trove of reasonable doubt, even if denied access to the data (which, in itself, would be a point of reasonable doubt).