I feel that these are interactive stories that anyone can add to for a reason. If an episode actually contributes to the story line in some way and isn't a flame, total and intentional branch-killer, or just 'filler' a few words long, then I say go for it.
Take your creativity by the horns when it strikes, and do what you feel like doing. If it isn't what the original author intended, so be it! There isn't any set number n new additions to an episode as far as I know, and myself, I enjoy being surprised by the directions someone takes something I write.
Plug continuity holes, correct mistakes or oversights, redirect the flow of things in a way that pleases you...so long as you are adding to the story as a whole, I see no problem with it at all.
Maybe a flash of inspiration strikes one of the characters, or an offhand comment from an 'NPC' sparks a revelation? A fortune cookie provides a helpful hint, or they plunder onto it by sheer dumb luck, having meant to do something else entirely? Use your imagination and there is no limit to what might happen. Try to make it not seem too contrived, or like the author just decided "Bam, baby! Get out of jail free card!", if you know what I mean.
It is better to go with your gut and actually create something new than to sit back and watch opportunity pass you by in any case.
Mind you, this is simply my own opinion on the matter. Hope you find it helpful or at least entertaining.
