Setting variables using runtime api

I am trying to use a variable to fail haproxy health checks
monitor fail if { var(proc.is_healthy) eq 0 }

We run 4 HAProxy processes. When I send command to set is_healthy to 0, then health checks from some processes still return 200, I have to repeatedly set variable to zero hoping that it has been set to zero in all child processes.

Is it possible to send command to each child process?

HAProxy Version 2.4.17