User-Exit-Include Question

Hi all.

I've found in the documentatiion that the User-Exit-Include RPREX000 contains various different user exits (form routines), that allow me to set up the settlement process, but this is and standard include, if I try to mdify it sap asks me for an access key to the object.

I just wannn know how this User-Exit-Include RPREX000 works and how can I modify it.

Best Regards.

Gregory.