Actually, if you change the item such as the Google LOGO to Grayscale, adjust the contrast so that there are no saturated blacks, this can be done in levels and in contrast adjustment, you can then colorize to red which will boost your colors back up to normal, then Adjust/Color Balance/Red/Blue/Green, turn the Red to 100%, the Blue and Green to 0%. Then copy the first "o" in Google and paste over the formerly yellow "o" and you have done it.

However, if the purpose is to create a printable file where everything will print in one color at a commercial printers, once you have achieved the Grayscale and balanced the gray, do all the artwork that needs to be printed in the same grayscale mode and let the printer print it in the color of your choice.