D/l here : http://cybercreator2.free.fr/Pythons/camera_changer.py
It’s made for be added to the directory of the 2.34’s scripts library.
Then you can launch it in blender by the script menu for objects.
Next, to use it, just name your cameras with the name of its changing frames.
For exemple a camera named “1,25” will become the default camera at frame 1 and 25. Another camera can be named “12” and will become default camera at frame 12, etc…
So I hope you understand my bad english and that this script can be usefull for some