Expert PHP coder to modify a Moodle class

We need an expert PHP coder to modify a Moodle class object, to obtain the grade report Excel in the best format, the file to be modified is attached (moodle_root/grade/export/xls/grade_export_xls.php), and the xls file to be built is also attached (in written spanish).
Please, use the lastest version of Moodle.

I will only accept proposals that start with #IamMoodleCoder the rest will be eliminated