In RB the style only affects the next generation process. So changing it has no effect on existing tracks, only the tracks selected the next time you hit generate.

I generally cut/paste or mix/match sections to get what I want. It can seem like a pain, but offers great flexibility once you get the hang of it.

Keep the sections from your new (no fills) track that you like and paste in the fills from the other track that you want.
I find it faster to start with the simple track and add (paste) the fills where I want them this way.

I do not work here, but the benefits are still awesome
Make your sound your own!