I know very little about Poser material nodes, but think I may have a solution to the problem, if I have understood the question correctly.

As I understand it you want to be able to make various parts of the hair invisible, without affecting any other material settings.

Start by making all of the hair transparent by seting the "Transparency" value to one. At this point everything is transparent (there are no trans trans maps applied at this point). What we will do now is to divide the hair into parts that can be made visible individually. Each part that is to be made visible gets its own trans map, with the parts that are to be visible in white, or shades of grey, and all the rest of the map black.

These individual maps are then added together using Math Functions nodes, as in the above image. To make a part invisible, you turn its map off by setting the value where it plugs into the Math Functions to zero. In the apove image, Map_6 has been turned off, making the lower left corner invisible. The important thing to grasp is that you are adding or subtracting visibility, not transparency. In principle it is reletively simple, but in praxis the hard part is knowing which parts of the map relate to which parts of the geometry.