Hi Felipe,
Yes I think you may have to create you own change document object as changes are not saved into tables for your Z field.
You would create a structure with along with field that needs to be stored. This structure should also have fields to be used as key. Once structure is ready, create change document object in SCDO. Upon generation of this object, you would get function modules. You have to call *_WRITE_DOCUMENT FM from some place (Could be a BADI). You could refer the FM call which you already debugged to set the exporting parameters. Pass the change indicator accordingly. I am not infront of SAP system but if I remember correctly, 'I' for insert, 'U' for Update and 'D' for delete.
Let me know if you face any issue, I have already done this so will try to help.
Regards,
Sanjay
