As said, there is no 'System Wide' ICC application for Windows.
Only the VCGT (which can be part of the ICC) is system wide, but is only a 1D LUT, so ONLY affects the grey scale/white point.
When you open Photoshop, that will use the full ICC profile as it is n ICC aware program, so will manage Gamut.
to see a method for using ICCs with Photoshop.
The CLCalibrationLoader is basically loading the VCGT into the graphics card, just as SpaceMatch DCM does.
Exact the same as Calman Client 3.
As stated, this is just a 1D LUT, and ONLY affects the grey scale/white point.
However, some displays do use ICCs within them, matched to the OS ICC, for display calibration.
But, such calibration is just a 1D LUT, and 3x3 matrix.
They are not 3D LUT based.