You are correct.Just took a look at mine and it appears without further disassembly that the decocker is one piece, so it's doubtful that you could remove one side of it without cutting it. Anyone who has taken down their FCG to get a better look can correct me if I'm wrong.
Re cutting, you can cut it in the valley between the'fat' part and the little part with a Dremel tool then de-bur the cut and touch up the end with a little Perma Blue. Looks pretty good !!