Sorry forgot to answer where you can find the Advanced tab on your shader.

All you need to do once you have selected your shader is scroll down to the advanced tab, click on it and the Output Opacity will be there.

Step One, select the shader and in the Attribute Editor of that shader it will list all its
attributes.
Step two. Scroll down till you see the Advanced tab.


see the attahced image: https://imageshack.us/photo/my-images/89/oh14.jpg/