No, turning it exactly upside down in the x direction puts the pentagon on top in exactly the same orientation that it was to begin with, so you can still do an R.
For scrambling purposes, I found a way to drag my fingers across the surfaces so that there are 3 "shifts" that I can do that accomplish an x2. That way I can reliably do it every time without having to think about it much.
I'm so terrible at solving kilominx, but at least I'm pretty good at scrambling it.
I have a feeling that if we were to ever make it an official WCA event, we'd need a different scrambling method; this one is not very practical for official competitions - too confusing for anyone other than people who regularly do the event.