Is there a way to specify selected vias as tented/not tented? I know that this can be done globally in 'Layer classes' in technology, but this works globally. Can i somehow remove soldermask for a particular via that is used as a test point for example? Or bind to to via style somehow? I mean other than just placing a round shape on soldermask layer.
You can have selected vias tented or untented by using two different pad styles for vias in your design.
First of all don't set up tented vias in the Layer Classes but have all vias exposed all the time by default.
Create two different pad styles for your vias.
For the non tented via just have a normal pad style of, say round pad 0.65 mm with a 0.30 mm plated drill. Pad Naming style for this using the IPC rules would be v65h30.
For the tented vias just have a pad style of round pad 0.65 mm, with the 0.30 mm plated drill, but this time use the By Layer button and select Solder Mask Top (or whatever you've called your solder mask layers) and change the size to 0, then use the By Layer button again to do the same for the Solder Mask Bottom layer. Pad Naming style for this using the IPC rules would be v65h30m0.
Use the tented via v65h30m0 as the default in your design, but when you want an untented via just select it, change style, and select the untented via v65h30.