Signs point to yes.
Creator JMS replied on Usenet and mentioned this regarding the first time this particular portion of the vision is shown (Londo talks about it earlier, but the audience first sees it in Season 2, Coming of Shadows). Quote lifted from the archive at the Lurker's Guide:
I ended up giving Peter info on "Signs" prior to shooting "Chrysalis" last season; that was the biggie there. For "CoS" in order for the scene to match what's going to happen several years down the road in the series, I had to kinda give him the context of the dream, and what was really happening in that scene, and what caused it, and how he got to that place with G'Kar's hands around his throat.
He seemed quite...astonished.
A later comment regarding the payoff from War Without End:
I seem to recall, after that Londo/G'Kar scene was shown the last time, posting somewhere that folks now knew what has happened, but they don't yet know the context. Very few picked up on that and thought to actually reverse what they thought they were seeing to what they might be seeing.