Could this be a Mumsnet campaign? All products carry a flash on the front of the product with 'recipe changed' and the date on? This would be a quick visual check for us to either re-check all the ingredients if we haven't bought it for a long time or to know that nothing has changed if we have bought it since that date
Funnily enough Jodie I was thinking similar when I woke this morning, though I expect there may be some sort of campaign already, when Ive some time I intend to look into it further, because something does need to be done.
Its okay saying read all the labels & when its life threatening I doubt anyone ever takes their foot off that particular pedal, but when its brands you know & trust, especially if like us you rarely buy much in the way of processed stuff, its easy to be lulled into a false sense of security with those products. It stupidly didn't occur to me that an ingredient change wouldn't be marked as such - this popcorn now also contains soya, something I often see highlighted as its a common allergen, so I still feel the company is in the wrong for doing this so sneakily, or more so the legislation is wrong that allows it to go on.
I have learnt my lesson however & won't trust known products again & will make sure DD understands that herself & always reads all labels too, & where possible stick to making my own as I usually do. Yes I should of checked, but where is it right that any of us cant just trust these companies & have to repeatedly do that
Reading up on this particular artificial sweetener makes it even worse, they promote it as almost natural as it starts off as sugar, but wrapped in chemical compounds that don't break down in everyone's body - doesn't break down in water treatment plants either - which is a worry 

More worrying still is the fact that it was down graded from "safe" to "caution" in 2013 after the only long term study done on it (by an Italian scientist) after it showed high rates of lukemia in rats
For those that ask - DD thankfully is okay this morning, though naturally exhausted & washed out as it was 1am before the worst of it passed - meaning she also couldn't handle taking her pain killers for the fractured elbow & 3 am before the colic like pain finally stopped all together - that was after 3/4 of a pack of popcorn - a mouthful gave me abdominal discomfort too.
& I'm sorry, I disagree that a polite note to Butterkist will have much effect, I think we all know that most of these companies only really sit up & take notice if they think they might be sued or get bad press, a polite note will probably get us a few vouchers for freebies, nothing more. I'm not interested in freebies, I'm interested in nobody else needing to needlessly suffer as DD did last night & recognition that we are only human, we can all make mistakes for all kinds of reasons & that the owness should be on these companies, not us as customers.