How to insert static transforms when reading a rosbag?

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I am trying to write the positions of my camera frame to a file for this I have following code:

for topic, msg, t in bag.read_messages(topics=topics):
    if topic == "/tf":
        tf_msg = msg.transforms[0]
        if tf_msg.child_frame_id == "camera_holder":
            write transform to file

Now this is working, but the problem is camera_holder is the false frame. I have a transform between camera_holder and camera but I don't know how to apply it without writing a transformbroadcaster and listener. I don't need a publisher and listener since I have control of all the code and ros is not even running. Is there a way to "insert" a static transform into my rosbag such that I could simply do: if tf_msg.child_frame_id == "camera": instead of if tf_msg.child_frame_id == "camera_holder":