Dynamic multiply_const_cc()

Hi,
I have one last question for today :). I have a GNURadio Python
application that runs two gr.top_block() flow graphs simultaneously on
two
different daughterboards (RFX2400). My dream is that B is running
forever
(using B.run()) sending a continuous series of complex numbers with the
following connect --> B.connect(gr.vector_source_c([],True),
B.multiply_const_cc(), True).

I want A to trigger a B.multiply_const_cc().set_k(multiplier) on some
event.
In this scenario, is there anyway, I could get A to trigger dynamic
B.multiply_const_cc().set_k(multiplier) without
“B.start()+sleep()+B.stop()+B.wait()”. Basically…(as it makes sense)
if I
do B.run(), the trigger never does the amplification. Can somebody
please
help me, if I m trying to do something that is obviously not possible :frowning:

Hopefully my explanation was clear. I can post the code, if necessary.

Thank you,

B.connect(gr.vector_source_c([],True), B.multiply_const_cc(),
usrp_sink_c).
Sorry