He virtually never did that, it's the English translators who often did that. Most of his published novels are "first draft" and no different in French from the publication in feuilleton.

The difference between the novels and the original feuilletons is that, in the last decades, French scholars have begun to return to the manuscripts that could be found (sent to printers etc., especially abroad) to correct all the mistakes and changes that had been made over the years by the feuilleton publishers and printers (they altered Dumas' text significantly in places), but as far as I know, translations in English of those corrected versions have not been made yet.

Dumas could very much use new English scholarly translations. The oldest translations are especially dubious. He was translated to read well in English for a popular audience, accounting for the fact the English popular audience wasn't the French popular audience. In the many chapters I've compared (with public domain English versions), translation is terribly unfaithful in places. A lot of descriptions are cut or shortened (a paragraph down to a sentence, in many places), a lot of historical references are cut or greatly simplified, some scenes with subplots are completey absent. Also, whatever required the translator to make some research about French culture or history is cut. I think a few English editions still use these translations, probably not all of them though.

So basically, with Saint-Hermine you probably get something much more faithful to the French text, and closer to the real Dumas, while with his classics, the text is altered and edited.