Gone through the community and found some threads are guiding add additional field to CR header and most of them are pointing to the documentation below.
This guide is using Z-table method to capture additional information. Tested in the sandbox and found that there are some limitations
1) The record created in Z-table even though the CR is not saved yet. And no rollback when the CR is close without saved.
2) The Z-table is not accessible by any API including governance API/Convenient API.
3) When performing the check, BADI UMSD_RULE_SERVICE, not able to read the additional CR header field by using API, seem like the only way to access them is reading from the database instead.
4) File upload/mass upload will be an issue as the those field can not be added by using gov API/conv API.
Just wondering is there any other better option provided by SAP that allow to add additional Z-field into the CR header without enhancing the data model? Thanks in advance.