Hello Marcel,
If you wish to change the accuracy for all the cameras (change the default accuracy for the chunk), use the following line:
PhotoScan.app.document.chunk.accuracy_cameras = (x, y, z)
where x, y, z are values in corresponding direction. Could be the same number for all three, of course.
To change the accuracy for certain camera use:
camera.reference.accuracy = (x, y, z)