For all functions explain after you to have install a catkin worspace with bag_tools

Function merge.py

Open a terminal, go to the location of the script and enter the command python merge.py inputbagfile.bag --output outputbagfile.bag --topics /tf you can give many input bagfile and topics.The topic /tf is an example of topic. The name of the output bagfile is not necessary, if you don't indicate a name the name of the output bagfile will be output.

Fonction change_frame_id.py

On one terminal run ros with the command roscore. On another terminal, go to the location of your files and enter the command rosrun autoware_bag_tools change_frame_id.py -o outputbagfile.bag -i inputbagfile.bag -t topicname -f frameid