Ed,
If you look at the notes/memo for the Blues Rock 128 Realdrums (lower right corner), it says....
1-a:SideStick, HiHat : The sidestick is played on beats 2 and 4 with the kick
1-b:Snare, HiHat : The snare is played on beats 2 and 4 with the kick drums on
What this means is that
1) the BLUE PART MARKER sections (1-a) will use the sidestick and hihat.
2) the GREEN PART MARKER sections (1-b) will use snare and hihat.
In other words, this style already has exactly what you need. All you need to do is click a couple of times on the bar number that is the first bar of your chorus until the color of the square around the bar number turns green.
When you have the green part markers in place, regenerate your song and you'll have have the change in drums that you're after.
If you'd like to find out a little more about part markers, the below link will take you to a short, 2 minute PG Music video clip on them. While the video uses an older version of BIAB, the principle is identical today.
https://www.youtube.com/watch?v=C6ViJ2691vURegards,
Noel