I found a solution myself:
As it seems, the remapping of the /tf topic is not possible. It's only suggested a few times on the web for recorded rosbags. Maybe remapping works there.
Maybe naoqi_driver is the cause - I can't remap any of the topics from this package!?
I ended up modifying the source code of the naoqi_driver package.
Main problem for me was that naoqi_driver publishes the visual odometry of the naoqi framework as an odom->base_link transform in tf.
So I just removed that line that publishes to tf.
The next problem was that the base_footprint frame was published as a base_link->base_footprint transform.
I wanted to publish my own odom->[robot] transform to base_footprint as it is easier to create the odometry with robot_localization on ground level.
The base_link->base_footprint transform was calculated by naoqi_driver based on the odom frame.
I changed the calculation based on the transform from base_link to r_sole and l_sole frames and published it in reverse direction compared to before (base_footprint->base_link).
Therefore the new base_footprint frame published by naoqi_driver is independent of the surrounding.
Then I could do my odom->base_footprint transform with robot_localization and map->base_footprint transform with rtabmap_ros.
I also experimented with robot_state_publisher + urdf but it didn't publish the static joints...