Photoshop - change greyscale to specific ink mix

[emucru]

I have a greyscale background that is mostly 100% K with a couple white lightening bolts throughout. I want the image to print 100% K with 20 % Cyan for a slighlty cool rich black. If I convert to CMYK my black mix will be really heavy. Is there anyway anyone can think of to convert my image to 100 K, 20 C?

[D-Frag]

Image>Adjustments>Channel Mixer

go to cyan, make it 120%

[D-Frag]

or a duotone, either way should work

[emucru]

In greyscale channel mixer isn't available and when converted to CMYK black changes to a really heavy black (c95, m85, y85, k85).

I thought the duotone would work too but when I import it into InDesign and convert all spots to pro the added Cyan still shows up as an additional seperation. I thought that was weird.

[Ovaltine]

In CMYK mode, use the channel mixer. Drop Yellow and Magenta out of the mix. Adjust the black and Cyan channels as you want them. It often helps to use the eye drop sampler tool for this. Place 3-4 of them in various places on the image-one in the darkest place, one in the lightest and the other 1 or two in mid tone ranges- to make sure you have a good mix over all.

[emucru]

Thanks D-Frag and Ovaltine, I played around with the channel mixer and its working well.