Enable rewrite username option on RDP in case of linked vault credentials

It is somehow possible to enable option to rewrite only username in case of linked vault directly on RDP entry or via user specific option, because now it is not possible or it is possible via user specific settings but rewrite both username and password. We need to keep pwd from keeper security and rewrite only username due to specific username string in Wallix Bastion PAM solution. If it will be possible using variables in case of username rewrite it will be great feature. Thanks