Add static text to the top bar in GNOME

Is it possible to add some text to the taskbar (e.g. just to the left or right of the date display), preferably just by editing a config file without having to install any extensions?

I am looking to do this because I log in using several different user names, don't want to have a different wallpaper/background for each of them, and want to be able to tell at a glance which user I am logged in as without having to start a terminal window. So something like the ability to display an "A" or a "B" next to the date, according to which user I am, would be great.

Since you want to avoid extensions and your session is Wayland,

add the below command to startup Applications,

gdbus call --session --dest org.gnome.Shell --object-path /org/gnome/Shell --method org.gnome.Shell.Eval 'var userName = imports.gi.GLib.get_user_name();\                                                                                                                            
Main.panel._centerBox.add_child(new imports.gi.St.Label ({ text: userName, y_align: imports.gi.Clutter.ActorAlign.CENTER }))'