You won't need to worry about breathing things in, because the 'chemicals' they will use will (probably) be just fine dust particulates that are often used as cloud seeders. Water vapour needs something to condense against (like the mirror in your bathroom), and this is, in effect, all they are doing.

As Gov has said, however, I think such large-scale manipulations are dangerous. Moral, I'm not so sure, but dangerous yes. Everything in the natural world is interconnected, like a food web. It only requires one missing aspect to f*ck everything else up. What happens to the rivers that, come spring, will now have 10x as much snow melt, and the places that usually have a good supply, that will have none. What about avalanche risks in the region where all this new snow will land?

It's too much for us to understand. There are connections we will never realise until we start playing around with it, and then it will be too late. What benefits we think will come from this are more than likely to be overshadowed by the disadvantages.