HI Chantele,
I feel there is one BADI, where we can modify the messages from back-end methods.
You can make use of BADI PT_GEN_REQ for this purpose. Following
method is provided in BADI for managing the messages.
MODIFY_APPLICATION_MESSAGES
Source : Leave Request Various Configuraton Steps - ERP Human Capital Management - SCN Wiki
Regards,
Tejas