Under the F5 option you can tell BIAB to change key at any bar. I just tried this and was a bit surprised not to see the chords automatically change at that point, but I suspect telling BIAB that the key has changed at that bar, combined with the manual adjustment of the chords to the new key, will permit the engine to recognize the new tonal center.

BIAB – 2025, Reaper (current), i7-12700F Processor, 32GB DDR4-3200MHz RAM, 1TB WD Black NVMe SSD, 2TB WDC Blue SSD, 1TB WD Blue, 2 TB SK NVMe, 6 TB External, Motu Audio Express 6x6