Most of the properties come from the Text Style applied to the C3D Label Style. Unfortunately though, there is no line spacing adjustment value.
Two possible workarounds:-
1. In the label style composer/text use multiple text entries and change the Y offset to make your spacing smaller or greater.
2. Go into the label style and copy to the clipboard the contents you want the width factor applied to. Paste this into an mtext object, apply the width factor and paste the mtext contents back into the label.