I dunno, all you puzzled people, Google is your friend, and specifically, Wiki, with all its acknowledged faults.
For “copha”, think “melted Crisco” (yeah, I know Wiki says there’s really no corresponding material in the U.S. but hey. Think maybe a combination of Crisco and butter, or something like that, something rich). And it says that Coco Pops are basically chocolate Rice Krispies, which if they aren’t on the market here currently, still I remember having them in childhood (1960s).
So you’ve got a variation on the basic “rice krispie cookie bar” recipe here, the one without marshmallows (people can, and do, incorporate Rice Krispies into cookie bars)–melt the Crisco, dump it in with everything else. Pour into 13x9 pan. Chill. Slice into pieces.
So it’s not a Rice Krispie Treat, the one with melted marshmallows and vegetable oil–it’s a different thing, a cookie bar, but without any flour, only fat and sugar basically, with the Rice Krispies and shredded coconut bound up in a chocolatey, fatty matrix.
The reason you don’t use chocolate Rice Krispies in this is because they have very little actual chocolate flavor, and actually I thought they were kinda bland and nasty, kinda “blech”. Cocoa powder gives you a much more authoritative chocolate “punch”.
I suppose you could use chocolate Rice Krispies if you wanted to, if you were stranded on a desert isle with only Coco Pops to use, but I’m guessing that the finished product wouldn’t be quite right. For another thing, you probably need the contrast between the vanilla-flavored Rice Krispies and the chocolate-flavored Copha, which you’d lose if the Rice Krispies were themselves blandly sort-of chocolate-flavored, kind of.
ETA: Icing sugar is just a finely powdered sugar, which you would need in order to have the sugar dissolve immediately in the melted fat, which ordinary granulated sugar wouldn’t.