The purpose of this is for test points.
On a BGA fan-out I want to drop a via for an array of unused pins for this prototype run so I have the flexibility to hack and slash afterwards. To mitigate shorts, I'd like to have the vias/test points tented on the BGA side and exposed on the reverse.
On the properties menu of the via I can see the Top Solder and Bottom Solder layers listed but I'm not seeing an option to modify these individually.
I was looking for a textbox to specify the solder mask diameter, but didn't notice the check boxes on the bottom right to force tenting on the bottom or top.
This issue is resolved.