Hello paw.wiacek,
To clear the location accuracy you can use the following code:
#for cameras
for camera in chunk.cameras:
camera.reference.location_accuracy = None
#for markers
for marker in chunk.markers:
marker.reference.accuracy = None
If you need to set individual accuracy for certain cameras/markers, which shouldn't be related to the default chunk.camera_location_accuracy and chunk.marker_location_accuracy, you can do it in the following way:
camera.reference.location_accuracy = Metashape.Vector([x_acc, y_acc, z_acc])
marker.reference.accuracy = Metashape.Vector([x_acc, y_acc, z_acc])
So your second code block from initial post should work, if you change "camera.Reference" to "camera.referece" and "marker.Reference" to "marker.reference", providing that, of course, that Camera_location_accuracy, Camera_rotation_accuracy, Marker_location_accuracy are pre-defined as 3-component vectors (Metashape.Vector class).