I am trying to figure out if it is possible to fold/cut the X4 membrane to replace the membrane in an M2 chassis...
It's an interesting idea, but I think it would be non-trivial to make work. Definitely warranty voiding, and not for the timid...
That said, let me offer some thoughts on how you might make this work. First, the X4 uses a printed resistor in series with each switch, These are the black lines. Although the values aren't very critical, I suggest you don't try to fold or cut through them. If you must cut somewhere, you can cut the silver traces BUT you will need to reestablish the connection somehow. You won't be able to solder to the traces, so I would suggest attaching your jumper wires with conductive epoxy. Another trick I've used is to solder a wire to a small strip of copper tape with conductive adhesive, and then just press this on. This is a lot quicker than waiting for the epoxy to dry.
The X4 uses sealed membranes for a reason - it prevents humidity from entering and shifting the resistor values. If your keyboard is going to end up in a hot, humid place, you probably want to seal any cuts you make. However, you don't want to seal them completely - if you do, you can inflate and deflate with changes in barometric pressure. So you want to leave small vents. If you look carefully, you can see that these are designed into the membranes.
Anyhow, I hope this is helpful...
