\relative c'' {
  \override Stem.details.beamed-lengths = #'(2)
  a8[ a] a16[ a] a32[ a]
  \override Stem.details.beamed-lengths = #'(8 10 12)
  a8[ a] a16[ a] a32[ a] r8
  \override Stem.details.beamed-lengths = #'(8)
  a8[ a]
  \override Stem.details.beamed-lengths = #'(8.5)
  a8[ a]
  \revert Stem.details.beamed-lengths
  a8[ a] a16[ a] a32[ a] r16
}