Hi Claude,
unfortunately Band in a Box is not a real time arranger; you have to type all the chords before (via computer keyboard) then, when the song is complete, you can save it and hear what you have programmed, but you are stuck to the same chord progression unless you change it (again via computer keyboard). However, you can change the style (i.e. from Swing to Bossa or whatever you want) and the Tempo, but that's all; after a while it becomes pretty boring, especially because the styles are not exactly thrilling. The definition of "canned music" is appropriate, in my opinion.