@Hola Ola Please do not make any changes in hr_ServicesUtil this is an OOTB script include and it is not recommend to make changes in OOTB script include.

To address your requirement.

You can create an onBefore Insert business rule on Employee relations case and set the short description field using script as follows.

current.short_description = current.hr_service.name+ ' for  '+current.subject_person.name;

Hope this helps.