I have never found a subtitle style sheet for music lyrics like subject line says, there are some variables

1.) Make the music cleff in Subtitle Edit

open or close brackets

open or close parenthis

italicize for on or off screen

close the line with another cleff symbol

Professional theatre sites seem to have this down but as I'm doing a job it's totally confusing. I've seen subtleties like
someone sing off stage in Italic then emerge on stage where the lyric line changes to plain text and brackets or parenthis
but I cannot keep all thse hyrogliphics straight.