\version "2.19.35"

#(define transposing-score #f)

optionalTranspose =
#(define-music-function (parser location transposing-clef concert-clef from to music)
  ( string? string? ly:pitch? ly:pitch? ly:music?)
  (if (eq? #t transposing-score)
   #{
     \clef #transposing-clef
     \transpose #from #to #music
   #}
    #{
      \clef #concert-clef
     #music
   #}
   )
  )

\optionalTranspose treble bass bis c'' \relative c { a b c d e }

#(define transposing-score #t)

\optionalTranspose treble bass bes c'' \relative c { a b c d e }