calendar module customization

Is there any option to do customization on Calendar module to newer version 9+

Requirement :  In calendar module > Shared > Userlist > Select Filter user list by team >  Users (Select users for calendar display)
User list option in Users (Select users for calendar display) section is should be in alphabetically sorted. 
I have tried to achieve this requirement by changing default files. And its working fine as expected. But for upgrade safe need to do our changes in custom directory. 
I have made changes to default file and file is  modules/Calendar/CalendarDisplay.php
  1. To add Calendar module in studio, we have create studio.php (blank file) file and give permission and repair rebuild the instance.  - No Calendar module is displayed on Admin > Studio > Module_List
    File Path: modules/Calendar/metadata/studio.php
  2. To execute custom file, We have create Calendar module folder on custom directory and copied modules/Calendar/CalendarDisplay.php file from default directory to custom  directory i.e. custom/modules/Calendar/CalendarDisplay.php - But custom/modules/Calendar/CalendarDisplay.php file is not executed (We have checked via printing logs to sugarcrm.log file)
 Is there any option to do customization for Calendar module.