Assuming that when you PRINT SEPARATIONS, the bits you want in a metallic ink print on a unique separation then you don't need to do anything. And, you should be able to adjust the colour - assuming the tiff is set to Black and White or Grey... or you used to be able to when I was a print designer (back in 1995 with Illustrator v3 or something...
>> picks up walking stick and complains about RSI, and other medical complaints <<