Ok so that is what you want.
If I don't succeed to do it with the first shot,
I select the "rec" for the drum style part (or any other style part) but move the pan in center position agian of the style part I was wanted to change before I press the "play" style button.
Now the channel (style part) I want to change is at the center position again.
Now I can try once again.
Sometimes is not good the beginning of the pan to be at the center.Could start from left.
And sometimes I need to count so it can follow the beats of the style.
E.g,:
Beat 1 left
Beat 2 center
Beat 3 right
Beat 4 center
(One bar style)
If you succeed in just one bar you can copy the values to the next bars if all bars of the style are playing the same midi pattern.
I have a psr so, in Genos search for something like Channel-Bar Copy (it is also in style creator)
In that "Channel" tab there must be also an option "Remove Event" so you can also remove a "wrong" pan attempt from there if you wish for the style part.
Edit:
For the volume I didn't succeed also to do it this way.
I had to go inside the "Edit" tab of style creator and insert events as Dereka said