It is very simple dude, depending one the base shader. For this example I took a blinn material and added a checker map to is specular. The idea is the same as if you use an image to represent the specular. Under your spec, when you place an image if you open the attributes for the image there is a section called Color Balance. If you open that drop-down you will find Default Color, Color Gain, and Color Offset. If you tweak these values you can very quickly and easily adjust the influence your image has on the specularity. If that is not the look you are going for and you want the image to be more/less transparent on your specularity then adjust the Alpha values in the same section.
Keep in mind though that only Greyscale values will affect the specularity. So if you are applying an image convert it to greyscale to achieve the look you are going for.