Swap out GR processing blocks on the fly?

MAX = 10000

class my_top_block(gr.top_block):
  def __init__(self, peak_hold=80):
    gr.top_block.__init__(self)
    self.sample_rate = 10e3
    self.s = gr.noise_source_f (gr.GR_UNIFORM, MAX)
    u = foo.peak_fv (MAX, peak_hold)
    self.connect(s, u)
    self.v = foo.wait_vv ()
    self.connect(u, v)
    self.t = gr.null_sink (4 * 1024)
    self.connect(v, t)

  def set_peak_record(self, record, peak_hold=80):
    self.stop()
    if record == True: 
      u = foo.peak_record_fv (MAX, peak_hold)
    else: 
      u = foo.peak_fv (MAX, peak_hold)
    self.connect(self.s, u) 
    self.connect(u, self.v) 
    self.start()