Tune decay branching ratio in MadSpin

Dear MG team,

I am running MadSpin to simulate the decays of two stops in a SUSY event, one into a b+W+neutralino decay and another into a c-quark + neutralino. Ideally, I would like to force MadSpin to simulate these decays such that the stops decay 50% of times into the bW mode and the other 50%, into the charm mode. My MadSpin card is:

set max_weight_ps_point 400 # number of PS to estimate the maximum for each event
#
import model tcMETUFO /afs/cern.ch/work/a/alopezso/private/simulationMC21/run/PROC_tcMETUFO_0/Cards/param_card.dat --bypass_check
set seed %i
set spinmode none
# specify the decay for the final state particles
decay sq1 > c chi
decay sq1 > b w+ chi
decay sq1~ > c~ chi
decay sq1~ > b~ w- chi
launch

and I also attach the param card. The result is a 82% of events where both stops decayed into bW, 1.1% of times into cc+2neutralinos and the rest, one bW and one charm. Do you have any feedback on how I can modify the branching ratio used by Madspin ?

Kind regards,

Alvaro Lopez