The first is possible now. Av mode, and Custom Controls to switch the QCD to ISO (see p. 341). With that, ISO is set during metering only. With that setting in M mode, you set aperture/shutter when metering is inactive, and once you start metering you can adjust ISO.
- Give ISO the same importance as time and aperture (e.g. put aperture on one wheel, iso on the other, and time in auto).
- Sometimes I want to simply change a custom-mode from e.g. Tv to M or similar, which doesn't seem possible (please correct me if I'm wrong).
You can't change the base mode of a C# setting. Canon could fix that for the 1D X, it seems to be a legacy of having a mode dial (the 1D X is the first to have C# settings and no mode dial).
Thanks for the hint regarding the ISO controls, that will be useful, and I'll read the manual again for other treasures that I might have missed. (All in all the customisability of the 1DX is really good compared to what I had before, and I'm glad to have made this upgrade.)