Subscribing to message and re-publishing only specific part, real time?

edit

I ended up basing my solution around @mohsen 's answer:

Node file:

#!/usr/bin/env python
import rospy
import importlib
import math

from sensor_msgs.msg import JointState  
from inmoov_urdf.msg import JointAngles
from std_msgs.msg import Int16MultiArray
from std_msgs.msg import MultiArrayDimension


global pub;

def main():
    global pub;
    rospy.init_node('joint_angle_publisher')  
    sub = rospy.Subscriber('/joint_states', JointState, callback)

    pub = rospy.Publisher('/joint_angles', JointAngles)  
    rospy.spin()

def callback(msg):  
    global pub;

    out = JointAngles();
    out.angles = normalise(msg.position);
    pub.publish(out);

def normalise(pos):
    to_return = []
    for i, val in enumerate(pos):
        if(i == 0 or i == 3 or i == 4 or i == 22 or i == 23): # shift by +pi/2
            to_return += [math.degrees(val+1.5707)];
        elif(i == 1): # shift by +pi/4
            to_return += [math.degrees(val+0.7854)];
        elif(i == 2 or i == 5 or i == 24 or i == 25): # abs
            to_return += [abs(math.degrees(val))];
        else:
            to_return += [math.degrees(val)];
    return to_return;   

if __name__ == "__main__":
    main();

with JointAngles.msg being:

int16[] angles

Thank you @gvdhoorn and @mohsen for your input :)