Nope, when water gets in it, you change the fluid. You can add isopropyl alcohol to fluid, but it will just let the water mix with the oil, which is even more of a mess and bad for the internals of the pump. Steel springs and check balls don't like water.
There is this stuff in a red plastic bottle (don't know the name), but they say it is guaranteed not to freeze. I think it's called somethign Marvel Mystery fluid (not kidding). I've seen it at Wal-Mart.
Change the oil in your pump AND plow cylinders every year before the start of the season. Most people just change the oil in the pump cause it has a big ol drain plug on it but most dont change the oil in the cylinders. Those cylinder accummulate condensation during the spring, summer and fall and then gets misxed into the nice clean pump oil the first time you angle the plow. Then it gets nice and cold and boom frozen pump.