% a music function to convert manually typeset beams: [ ] ...into slurs: ( )

beamsToSlurs =
#(define-music-function (music) (ly:music?)
   (music-map
     (lambda (m)
       (if (not (null? (ly:music-property m 'articulations)))
           (for-each
             (lambda (a)
               (if (music-is-of-type? a 'beam-event)
                   (begin
                    (ly:music-set-property! a 'name 'SlurEvent)
                    (ly:music-set-property! a 'types
                      (append
                       (delete 'beam-event (ly:music-property a 'types))
                       '(slur-event)))
                    (ly:music-set-property! a 'spanner-id ""))))
             (ly:music-property m 'articulations))
             m)
       m)
     music))

%%%%%%%%%%%%%%%%%%%%%%%%%

music = {
  \time 2/4
  | c'8[ d'] e' f'
  | g'[ a'] b' c''
}

words = \lyricmode {
  la li lo 
  la li lo
}

<<
  \new Staff \with { instrumentName = "Traditional" } 
    { \autoBeamOff \music }
    \addlyrics \words
  
  \new Staff \with { instrumentName = "Modern" }
    \beamsToSlurs \music
    \addlyrics \words
>>