[mpl]

Toggle bypass selected tracks envelopes:

  function main(state) local tr    
    for i = 0, reaper.CountSelectedTracks(0) do
      if i == 0 then tr = reaper.GetMasterTrack(0) if not reaper.IsTrackSelected(tr) then goto skip end else tr = reaper.GetSelectedTrack(0,i-1) end    
      for env = 1,  reaper.CountTrackEnvelopes( tr ) do
        local tr_env = reaper.GetTrackEnvelope( tr, env-1 )
        local retval, env_chunk = reaper.GetEnvelopeStateChunk( tr_env, '', false )
        if retval then reaper.SetEnvelopeStateChunk( tr_env, env_chunk:gsub('ACT [%d]', 'ACT '..state), false ) end
      end
      ::skip::
    end
    reaper.TrackList_AdjustWindows( false )
    reaper.UpdateArrange()
  end

  local _,_,sectionID,cmdID = reaper.get_action_context()
  local state = reaper.GetToggleCommandState( cmdID )
  if state == -1 then state = 1 end
  reaper.SetToggleCommandState( sectionID, cmdID, math.abs(1-state) )


  reaper.Undo_BeginBlock()
  main(state)
  reaper.Undo_EndBlock("Toggle bypass selected tracks envelopes", 0)

(there is a little bug in REAPER GUI: bypass button isn`t updating its state after actual bypassing envelope)