Shader.SetGlobal for properties that materials already have

According to the unity script reference, the Shader.SetGlobal functions can only set properties that the material doesn't already have. Ex: if I had a material in the scene, and that material uses/used a shader that has a property called "_Theta"(float), if I call Shader.SetGlobalFloat("_Theta", 0.5f) it will not work for that material. Well, that's a big problem for me since I wrote some shaders and now I realise the cost of looping through the entire material list of the scene is pretty expensive( a 15-20 fps drop if I loop through all the materials and set floats for materials one by one), I modified my shaders(deleting the _Theta property in the property block) but now the materials(about 200 of them) I created with the old shader still has _Theta as a material property, I could remake all the materials again but that would take a lot of time, is there anyway to cleanup a material so that it will only have the properties that the current shader exposes?