You shouldn't need any sscr key for this requirement
- F4 : Use BAdI WBS_USER_FIELDS_F4 (SE19)
- Check : Use some PS validation on WBS (OPSI)
For the "without Access Key" assertion, remember that those keys depends amongst others of basis releas, so you may be no longer allowed to change object, but modificaiton may have been kept during SPDD. If your S-id is allowed try to check for a previous sscr key at https://support.sap.com/sscr, "lauch the sscr application", "My Company's Registrations".
Regards,
Raymond