If you're familiar with other sequencers, you could also drag'n' drop or export the BIAB song as a midi file and do your rearranging there. A nice feature is the ability to export the drums to separate midi files, so it's easy to know exactly which drum you are working on. When you've got it all tweaked you can then export the midi file from the other sequencer and reopen it in BIAB. The whole multichannel midi file will now be on the melody track.

You can then use the 'automatic style wizard' to make a new style from the tweaked midi, transporting your new drum arrangement into a new style for handy use at any time.

If you just want to improve the drums for a specific song ... If you've learned your GM drum notes, i.e., 35 = acoustic kick = B0, 36 = regular kick = C1, etc., you can rearrange on either the piano roll or the Notation Window using the Editable Notation window. You can activate the little speaker icon in the latter to left click and scrub the note with the mouse pointer to identify which drum sound it is. I haven't gotten into it very deeply yet, but I am sure you can add, rearrange and do all the normal editing stuff. Just look for help in the help files or tutorials.

Prado