In Band-in-a-Box you can do a Gm9 and a GMajor9#11, but not a Gm911. A full list of recognized chords are here: https://www.pgmusic.com/tutorial_chordlist.htm

You can write in your own custom chords either in the Piano Roll view or the Notation window. But when you write these in, it needs to be on a MIDI track (yellow or blue in the mixer). After making your own edits, you'll need to freeze the track so it does not re-generate. The freeze button looks like a snowflake (*) in the mixer.

This video goes over how to use the Piano Roll in Band-in-a-Box: https://youtu.be/7VnIIx3V4QY


Best,
Chantelle