code: public void setBeliefValue(String agent_name, final String belief_name,
              final Object new_value, Connector connector) {
  
          ((IExternalAccess) connector.getAgentsExternalAccess(agent_name))
                  .scheduleStep(new IComponentStep<Integer>() {
  
                      public IFuture<Integer> execute(IInternalAccess ia) {
                          IBDIInternalAccess bia = (IBDIInternalAccess) ia;
                          bia.getBeliefbase().getBelief(belief_name)
                                  .setFact(new_value);
                          return null;
                      }
                  }).get(new ThreadSuspendable());
      }
docs: This method changes the value of an agent's belief through its external
  access
  
  @param agent_name
  The name of the agent to change a belief
  @param belief_name
  The name of the belief to change
  @param new_value
  The new value of the belief to be changed
  @param connector
  The connector to get the external access