We were under the wrong impression, that CORSIKA, CERES and we use different Azimuth definitions.
As it turns out, CERES and FACT-Tools use the same (N = 0, E=90°), the transformation in CERES of (180° - CORSIKA AZ) happens because corsika gives the movement direction of the particle, which is opposite to the viewing direction of the telescope.
So we should not reverse this transformation to get simulations with the correct magnetic field for an azimuth value.
maxnoe
commented
4 years ago 
We were under the wrong impression, that CORSIKA, CERES and we use different Azimuth definitions.
As it turns out, CERES and FACT-Tools use the same (N = 0, E=90°), the transformation in CERES of (180° - CORSIKA AZ) happens because corsika gives the movement direction of the particle, which is opposite to the viewing direction of the telescope. So we should not reverse this transformation to get simulations with the correct magnetic field for an azimuth value.