Can I spray peroxid??? (to have same layer everywhere)???
I don't think you'd want to do that. Peroxide isn't something you want getting on anything it shouldn't be on, so you'd have to be in a really controlled environment to start with. And then I just don't think you'd get any advantage out of it, because if you spray liquid hydrogen peroxide, it's just going to drip and dry anyway. The reason you use it as a paste is so it stays in place and takes a lot longer to dry.
It's not hard to use a brush to get an even coating of whatever paste/gel solution you're using. And anyway it's not so much an even coating that you need as it is just having at least some of it everywhere you need it. As a liquid, you're going to end up with totally bare spots where it's just dripped off.