According to the manual this action is supposed to do double duty. If the solder mask layer is on, it's supposed to change the soldermask clearance. If the soldermask layer is off, then it changes the polygon clearance.
However, I've found that ChangeClearSize(SelectedVias, 0mm) appears to set the mask aperture to 0.05 mm instead of zero. So this appears to be broken nonetheless.
Bert-
According to the manual this action is supposed to do double duty. If the solder mask layer is on, it's supposed to change the soldermask clearance. If the soldermask layer is off, then it changes the polygon clearance.
However, I've found that ChangeClearSize (SelectedVias, 0mm) appears to set the mask aperture to 0.05 mm instead of zero. So this appears to be broken nonetheless.