Hi Pawel,
Thank you for your idea to help us improve SDL TMS. At present, as you're aware, the Display Name for an SDL ID user is taken from the authenticating system. This is typically the ADFS implementation for an organization (such as SDL). Allowing this to be changed from the name provided externally could present a security risk so we have to tread very carefully here before allowing it to be changed. I'll put this under community review for further comment and voting.
Regards,
David