1. The batch processing dialog.
1.1 The "ICC convert" transformation should be placed under the "Convert" section, because that's what it does - convert between ICC profiles, possibly color modes (RGB<->CMYK).
1.2 There should be a batch "Attach ICC profile" that just stupidly attaches an ICC profile to an image without any kind of translation. Optionally overwriting already present ones. If "ICC convert" can already do that, it should be made clear somewhere/somehow, but i don't think it can.
2. ICC Information
2.1 The image properties (Alt+Enter) dialog should inform you about an attached ICC profile.
2.2 You (sometimes) need to rebuild your thumbnails to make the ICC overlay icons appear for (some) images.
2.3 A thumbnail label for the ICC profile is missing IMO.
3. General ICC options
3.1 It's not clear to me, if it's enough to simply activate color management, to let XnView use the currently configured Windows monitor ICC profile. Does it? Or do you have to explicitly specify it in the file select field right below the switch?
3.2 For performance reasons it might prove helpful if it was possible to disable ICC profiles for the browser's preview area (or other areas). Better performance would be preferred, of course.