Ah no you can't do it that way. Materials are everything in the material lab thus when you load one it replaces all the settings that you had before loading it. You have to adjust each channel seperately. To blend the materials you would have to note/write down each element that is part of that material and then apply it to one of the channels. The draw back to this is materials which use multiple channels will not be easily done. BTW each channel is a texture that is blended together to form a material.