How could humans alter storm intensity or direction other than cloud seeding?
There are numerous ways. Arguably, some we are already doing, but are not intended (such as urbanization and the emission of different pollutants). But I'll suppose you are wondering about intentional modifications. Moreover, this is perhaps too general of a question, as there are a variety of different types of storms, of varying sizes. I'll tackle what I can, in a reasonable fashion. And for the sake of argument, I'll just ignore the downsides.

Let me repeat that, I will ignore the downsides. This may yield a comedic effect.


Extratropical cyclones.


Being that these take the energy from baroclinicity, a good way of disrupting the intensity of these storms is to warm the cold area and cool the warm area. You can do whatever you want to do to accomplish that, be it drop a couple megaton nuclear bombs in the cold region, etc. 


Tornadoes


One thing you need to know about tornadoes is that the storms that generate these rely on stability/buoyancy and shear. Leveling everything should reduce the shear. Covering the surface with ice should also promote a more stable atmosphere.


Hurricanes


Hurricanes derive much of their energy from the temperature and entropy difference between the surface and the tropopause. Also, increasing the drag can reduce the wind speed. Different ways to do these can be found in NOAA. 

Certainly these aren't all the ways that the weather can be modified. But these are just some. Of course, anything we do may backfire. Extratropical cyclones serve a purpose-transporting energy and momentum. Even hurricanes move water vapor towards the poles. And to that, I'll quote Jeff Goldblum:


  ...[Y]our scientists were so preoccupied with whether or not they could that they didn't stop to think if they should.