I am looking to remap "black" colors to a specific spot color. I am having good results if the source color is CMYK Black 100. But I wanted to extend the change to every "black" in every color space and so far I am not really successful.
Could the "Select color range" action help you? There is a checkbox to search in converted values of other color spaces. So for example an RGB object could be (internally) converted to DeviceGray and then if the result is between 0% and 1% gray it would be considered black.