For my 5D MkIII, I've tried to create camera settings for HDR mode and store them in the Custom Shooting Mode (C1, C2, C3). It appears that Custom Shooting Mode is greyed out (cannot be selected). Could not find anything in user's guide that addresses this.
By contrast, settings for the very similar AEB shooting mode can be stored in C1, C2, or C3.
Has anyone tried storing HDR settings in 5D MkIII? Were you successful? How?
If this option is not allowed, why might that be? Could firmware be changed to allow this?