There are patents on everything, does not mean they are worth the paper they are printed on.
To be precise, we modify the weather all the time. In fact, every exhalation out of your mouth adds to a rain storm somewhere in the world at sometime. It is the water cycle. So you, without patent, are a weather modification machine.
Really, to the sense of modifying the weather TO A DEGREE that has a discernible difference, with a machine, is not really possible AND have no one know it. If it was, someone would have noticed it by now, and had a video on youtube......just like bigfoot.
In order to make a storm like Helene you would have to transfer more energy into the atmosphere than the storm would resultantly be, meaning you would have to have a machine that could release energy equal to 1000s of nuclear bombs...........and have no one know about it...........very very unlikely if possible at all..