Now, during a Kenpo class, I've taught a flow drill from Arnis, but I make sure the people know the difference. I don't pass something as Kenpo if it isn't.
I do the same, but if that drill becomes incorporated into the regular curricullum, when does it cease to be a arnis drill and become a kenpo drill? It may have its roots in another art, but so do alot of things in kenpo, but now its all "kenpo."
If I add a puter kepala or silat leg press takedown to the end of a tech, does it really become silat, or is just an illustration of push/pull mechanics or the use of a knee check? Me, I'd still call it kenpo, it just shows a bit of variation from the one generation before, and if that variation gets big enough, it seems to make sense to make it a new "style."