Grid lines: changing their appearance

The appearance of grid lines can be changed by overriding some of their properties.

\version "2.24"

\score {
  \new ChoirStaff <<
    \new Staff {
      \relative c'' {
        \stemUp
        c'4. d8 e8 f g4
      }
    }
    \new Staff {
      \relative c {
        % this moves them up one staff space from the default position
        \override Score.GridLine.extra-offset = #'(0.0 . 1.0)
        \stemDown
        \clef bass
        \once \override Score.GridLine.thickness = 5.0
        c4
        \once \override Score.GridLine.thickness = 1.0
        g'4
        \once \override Score.GridLine.thickness = 3.0
        f4
        \once \override Score.GridLine.thickness = 5.0
        e4
      }
    }
  >>
  \layout {
    \context {
      \Staff
      % set up grids
      \consists "Grid_point_engraver"
      % set the grid interval to one quarter note
      gridInterval = #(ly:make-moment 1/4)
    }
    \context {
      \Score
      \consists "Grid_line_span_engraver"
      % this moves them to the right half a staff space
      \override NoteColumn.X-offset = -0.5
    }
  }
}