You can find options for the project-wide appearance of octave lines on the Octave Lines page in Engraving Options.
The options on this page allow you to change the appearance of continuation lines, continuation labels, the numeral at the start of octave lines, the position of octave lines relative to accidentals and noteheads, and their staff-relative placement.
There are musical examples for many options to demonstrate how they affect the appearance of your music.