I do have some whiskey stones that I really enjoy in bourbon and scotch. You definitely need to limit the amount you add with them, but to be honest I usually don't even bother to use them anymore and go with the straight whiskey!
With Schnapps you might do better putting the bottle in the freezer, because it's not as strong as gin, rum, whiskey, etc.
I'd love to use the freezer, but we have a small one... and it is filled with food and meat... I think that the bottle would be a very unwelcome addition!