I believe this column is read-only, so you can only use it in Read steps (RDM Extender Reader, RDM Reader). If the reference is maintained exclusively through imports, you can create a regular column to store the user.

I see. Thank you, AKislyakov.

I have another question regarding the RDM History Importer; when importing data with this step, the data seems to go only to the HISTORY and ALL HISTORY view, even with some records having “Date to” as blank (so they are valid as of now). Do you know how to also have those records in PUBLISH and EDIT perspective?

To use RDM History Importer step you should first import current state using RDM Importer step and then attach relevant history using RDM History Importer. 
The RDM History Importer is rather unsafe step: it’s not incremental; it will not check your data; it will allow you to create inconsistent history.

The step should be handled with care, and I wouldn't use it if not absolutely necessary.

It works. Thank you, AKislyakov.

Hello @AKislyakov, you mentioned earlier that the RDM History Importer step is not recommended as it can be considered unsafe. Could you please suggest an alternative method for importing data along with its history onto RDM? Thank you