If not, then the answer is simply to dilute the brine with a little distilled or purified water.

Not that tap water wouldn't work, but you're playing with straight flavor here, use something known to be truly neutral.

Anyway, different concentrations of salt and vinegar will change the freezing point. This talks about using brines and such on roads.

Apparently exposure to any oxygen will lower the freezing point of pickle brine as well. Which is why the molds in OP's picture are airtight.