Set Global Specular via Script

Hi. How do i property change the smoothness of hundreds of individual pieces (meshes), each with it's own material but with the same shader (Standard). I want to change the specular value on all those pieces that use the same shader, is there a simple way of doing that? Im trying with Shader.GlobalFloat but it's does do anything. I have and Enviroment system and i need to change the specular of all those meshes so it's looks like it's raining, Thanks!