Changing the vertical stacking order of octave lines
You can change the placement of individual octave lines relative to other objects in the vertical stack by changing their tucking index value.
According to general convention, octave lines are placed outside all other objects, but there are some instances where they can go inside other objects, for example, inside a slur if that slur is longer than the octave line.
Procedure
Result
The placement of the selected octave lines in the vertical stacking order is changed.