All of the above would most certainly cause global chaos and not run into the thought of green fanatics vs oil rigs or turning arable lands into deserts. But
1. Is the world worth being in charge of after that level of destruction?
2. How would the corporates/conspiracy cabal communicate without satellites?
and
I could see the corporates living off tinned food in their armed compounds, but with enough starving people they'd be over-run by unarmed mobs just by weight of numbers despite all the stockpiled machine guns and missiles.
Yeah, I guess for "we want to re-engineer society" you could plan to bump off a lot of people by those ideas and then be the only ones with any answers and people have to accept your answer to get fed but......
Maybe I'm expecting the conspiracy cabal/corporate to understand too much.
I've done a fair amount of 17th century re-enactment, read/watched documentaries on a moderate chunk of social and technological development and our western lifestyle has taken centuries to build, is incredibly networked and dependent and would take a very long time to re-build.
A small example. In the 17th century needles were valuable - as metal was all extracted by hand and it took a lot of skill to make a fine needle. So any woman owning a needle kept it in a special carrying case. If your house caught fire and you grabbed stuff quickly as you ran out the door - it would be your needle, possibly your spinning wheel, any metal tool and your cast iron cook pot (if you were rich enough to have one).
So what I am getting at is if you decimate the planetary population, who will farm the food, mine the metal, run the factories, deliver the raw materials and the manufactured goods?
Also, mining of metal in 17th century level was pits into the ground. We've probably mined most of the surface available metal and any stuff that you can get at with basic tools.
There has been a ladder of development, with each step including better tools which enabled the next step.
So, if you are plotting a serious drop in standard of living for the whole world (or at least the parts of it currently living western lifestyle), then you would actually need to build a seriously defensible area first, with farms, factories and mines and ideally your own oil well. That way you have carrots plus a good supply of sticks to ensure you stay on top.
You might want to look at some of the websites relating to end of the world for ideas as well. I've forgotten the name but there are folks in the US in particular who've withdrawn from modern society, live up in the hills, refuse to pay taxes etc. Look at stuff on them maybe.
Or in other words I'm highlighting a whole additional set of problems for Omnis, loosely labelled "by how much is it practical for the conspiracy to break the world"? With the sub-set options of them getting the plans right, and them getting the plans wrong.
Final thought - if you are re-engineer society, you will need to keep a communications media of some form working in order to spread the word.