For questions regarding Surfice, please use the dedicated NITRC forums or create an issue on Github. 

The .node files use the simple BrainNet text format. You can use your favorite text editor or scripting language to concatenate two node files. The format lists six columns for each node:
  Xmm Ymm Zmm Color Radius Name
You could also provide a different "color" for your two sets of nodes. When you 

-9.631 28.620 33.320 1 1 L.superior.frontal.gyrus
10.801 28.312 33.032 1 1 R.superior.frontal.gyrus
-30.468 35.927 26.576 1 1 L.middle.frontal.gyrus
30.734 37.800 25.642 1 1 R.middle.frontal.gyrus
....
-10 28.620 33.320 2 1 L.superior.frontal.gyrus
11 28.312 33.032 2 1 R.superior.frontal.gyrus
-32 35.927 26.576 2 1 L.middle.frontal.gyrus
31 37.800 25.642 2 1 R.middle.frontal.gyrus
....

Then the you display the nodes in Surfice, you could differentiate the node by its color as shown in the screenshot.