How to "change the complete graph opacity to 30"?
There are two basic ways: using GRAPH OPTIONS to control the default setting for all edges and vertices and to use the Edit Selected Vertex (and Edge) Properties on any selected vertices (and incident edges).
This is the Graph Options dialog highlighting the Vertices Tab
This is the Graph Options dialog highlighting the Edges Tab
Modify the Opacity settings here to control the default for the Graph as a whole.
Alternatively, select all vertices with CTRL+A or select a sub-set of vertices with the selection tool (Click-Drag) and then right-click and select Edit Selected Vertex Properties and change the opacity:
This can be repeated for selected edges as well:
One additional alternative is to directly edit the opacity values in the Edges and Vertices worksheets. These columns may be hidden (by default) - use the NodeXL>Show/Hide>Workbook Columns>Visual Properties to reveal the "Opacity"column.
I hope this addresses your question - feel free to follow up!