...I'm pretty sure, using #VisualBasic, it should be possible.
The #footnotes issue I described at the beginning of this thread is probably the most difficult part.
But leaving that point aside, it is simply capturing the length of the whole text, subtracting the length of the #hashtags, the heading, and the subtitle(s), as well as of the credits ("via/by...") from the 500 limit and then cutting the total blog texts in segments.