Mel, I don't think you can.

This is probably something for the Wishlist.

If you would like to read more about how BIAB is determining this, take a look at the Opt., Preferences, Notation dialog window. In version 2011.5 at least, there is a checkbox for "Use Chord Scale for Enharmonics". The tool tip is not working but the Help for that screen says:

Use chord scale for enharmonics

The sharps and flats in Band-in-a-Box notation are context sensitive to the chord names. For example, if you are in the key of Eb, and the chord is E7, a G# note will show up as a G#, and not an Ab. This means that the notation accidentals will automatically show up correctly.

Enharmonics for chord tones are automatically based on the chord. Enharmonics for passing tones are based on chords if "Use Chord Scale Enharmonics" is set to true. For example, on an F#7 chord in the key of Eb, the Ab note is part of the F#7 scale (as a G#, the 2nd of the scale), but is also part of the Eb key of the song. If you want to display based on the chord scale, setting "Use chord scale enharmonics" will display the note as a G# instead of an Ab.

Having said that, using version 2011.5, I tried unchecking the box, and still got B/A#.

BIAB 2025 Win Audiophile. Software: Studio One 7 Pro, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Roland Integra-7, Presonus 192 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.