Adding a figured bass above or below the notes

When writing a figured bass, you can place the figures above or below the bass notes, by defining the BassFigureAlignmentPositioning.direction property (exclusively in a Staff context). Choices are #UP (or #1), #CENTER (or #0) and #DOWN (or #-1). This property can be changed as many times as you wish. Use \once \override if you don't want the override to apply to the whole score.