\addff (and \doaddfeature) no longer seem to work. What's the alternative to add/remove features on the fly?

MNWE:

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\starttext

\startluacode
  fonts.handlers.otf.addfeature{
    name = "fanum",
    type = "substitution",
    data = {
      [0x30] = 0x41  -- '0' => 'A'
    }
  }
\stopluacode
\definefontfeature[fanum][fanum=yes]
  {0123
    %\addff{fanum}
    \doaddfeature{fanum}
    0123  %% does not work
    \definedfont[dejavusans*fanum]
    0123  %% works
  } 0123

\stoptext

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