A bit of advice about the way you are working - i think the drums issue is dealt with above. If you really want to start from scratch use RealBand not BIAB. You can add tracks as you like and choose midi or real tracks right from the start without erasing everything as you are doing in BIAB. In RB you don't need to start with a style. Just choose a key, time signature and tempo. Then search for the instruments you want.

You start with a clean slate rather than fight the way BIAB works. Mind you, I'd be surprised if you can't get a rough mix almost like the one you eventually want in BIAB. Choose the right style, tempo and key. The stylepicker lets you choose by genre,time signature and tempo and even by song name if you know the feel or sound you are looking for. Generate the track then if you don't like it choose another style till the track is close.

Save the file, open it in RB and then tweak the instruments as you like. Rather than start completely from scratch you'll find a lot of the BIAB generated tracks are fine. I often change guitars but find the bass, piano and drums are often fine as they are if i've chosen the right style.