Raising Exceptions in Subscriber Callbacks

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ROS distribution: noetic, rospy

I want to raise specific exceptions depending on the data received from the rostopic. However, raising exceptions in the subscriber callback (user_callback) returns a bad callback error due to rospy callback exception handling: https://github.com/ros/ros_comm/blob/...

Is there a way to raise custom ROS exceptions in one node (user_command node) and handle it in another (control node)? Or is there another way to filter data from a subscribed topic and raise an exception accordingly?

For example: I am subscribed to /user_commands. If a "t" is published I want to immediately exit the "scan" state while loop and switch to another state (track)

class command_t(Exception):
    pass

class command_h(Exception):
    pass

class command_hv(Exception):
    pass

class actions:
    def __init__(self):
           #initialize all my variables

    #CALLBACKS
    def user_callback(self,msg):

       if (msg.data == 't'):
           rospy.loginfo(msg.data)
           raise command_t #BAD CALLBACK ERROR
       if (msg.data == 'h'):
           raise command_h


    #STATES
    def scan(self):
        try:
           rospy.loginfo("scan mode")
           local_delta = 0
           while (x0 + local_delta < x1):
               self.waypoint(x0 + local_delta, y0, z)
               self.waypoint(x0 + local_delta, y1, z)
               local_delta = local_delta + self.delta
               self.waypoint(x0 + local_delta, y1, z)
               self.waypoint(x0 + local_delta, y0 , z)
               local_delta = local_delta + self.delta
           local_delta = 0

       except command_t:
         self.track()
       except command_h:
          self.home()

if __name__ == '__main__':
    rospy.init_node("control")
    action = actions()
    user_sub = rospy.Subscriber("/user_commands", String, action.user_callback)

    rate = rospy.Rate(100)
    action.scan()