With kicad v8 there is the global option “Tent vias” in the gerber plot dialog. This affects all vias on the complete board, and affects only the gerber output files, not the 3D-view.
If you want a individual setting for via tenting then you have to wait 2 month until the upcoming version kicad v9 is released. This thread shows the announcement of the feature: Post-V8 New Features and Development News - #20 by craftyjon