Changing the breath mark symbol

The glyph of the breath mark can be tuned by overriding the text property of the BreathingSign layout object with any markup text.

\version "2.24"

\relative c'' {
  c2
  \override BreathingSign.text = 
    \markup { \musicglyph "scripts.rvarcomma" }
  \breathe
  d2
}