Copy & Paste blend modes and opacity
Not only can you copy-and-paste layer styles from one layer to another, but you can also use the same method to copy blend modes and opacity to multiple layers. Just pick the layer that has the blend mode and/or opacity setting you want, and Control-click (PC: Right-click) on it and choose Copy Layer Style. Then select all the other layers you want to share the same setting, Control-click again, and this time choose Paste Layer Styles.
comes in very handy