Commented text showing how to hack a label size change.

gephi-sigma-edge-props.json

{
  "sigma": {
    "drawingProperties": {
      "activeFontStyle": "bold",
      "defaultEdgeType": "curve",
      "defaultHoverLabelBGColor": "#002147",
      "defaultLabelColor": "#000",
      "defaultLabelHoverColor": "#fff",
      "defaultLabelSizeComment": "Changing 'defaultLabelSize' doesn't change the default label size if 'fontStyle' is at its default, 'bold'. Stripping that value allows for adjustments.",
      "defaultLabelSize": 16,
      "defaultLabelBGColor": "#ddd",
      "font": "'Museo Sans'",
      "fontStyleComment": "Default for fontStyle is 'bold'. For some reason, with that, changing 'defaultLabelSize' doesn't change the default label size. Stripping it allows for adjustments.",
      "fontStyle": "",
      "hoverFontStyle": "bold",
      "labelThreshold": 0
    }
  }
}