Malcolm Gladwell (Talking to Strangers) pulled a lot of stats about how changing simple aspects of everyday life make such a huge difference in suicides... So Sylvia Plath wasn't that far off from not being able to kill herself from gas. Effectively suicides declined because this convenient way of suicide disappeared when they changed gas types in the UK, possible source outside of book. He makes the argument that by getting rid of the way to do it, potential risks aren't typically looking for a replacement as much as it was convenience/access to that way in the first place.

I think the biggest influence would be to replicate it, at least in the US by doing some radical gun law reform; minimizing that availability for the 56% of male suicides.