On the Surface Tab click on the Diffuse Strength arrow and select Layered Image Editor to get the LIE interface. Then you will see the Opacity slider. You will be prompted to save after you are done with your changes. Give it a unique name, it won’t change your original layer. Now when you reopen your scene your layers will load with your edited settings.
Thank you SimonWM. this was very helpful and the screenshot illustrated it perfectly.
Thanks ya’ll for your help. I now understand what folks are talking about when they say to click on the little arrow. I was having trouble finding that.