-- Send a message to the console
function msg(m)
    reaper.ShowConsoleMsg(tostring(m) .. "\n")
end

-- START HERE vvvvvvv
if reaper.CountSelectedTracks(0) > 0 then
    local first_sel_track = reaper.GetTrackGUID(reaper.GetSelectedTrack(0, 0))
    reaper.SetProjExtState(0, '4PointCut', 'dst_track', first_sel_track)
end