I got some support on this:
Go to Options > Toolbars and open your custom toolbar File > Open… in the top menu.
Make sure that the toolbar group is ticked. Back in Rhino, make sure that the new toolbar is visible and docked where you want it.
%AppData%\McNeel\Rhinoceros\6.0\Plug-ins\Toolbars (dc297053-96c0-4883-a688-8326b4e024a8)\settings\ settings-Scheme__Default.xml
%ProgramData%\McNeel\Rhinoceros\6.0\Plug-ins\Toolbars (dc297053-96c0-4883-a688-8326b4e024a8)\settings\ settings-Scheme__Default.xml
This will enforce that the loading of that toolbar setting next time (and every time) that you open Rhino, even if a user closes that custom tab. If you copy this file to another computer, and the path of the toolbar is accessible to that computer, the toolbar should load.
There are a few considerations:
First, every change that you make to the toolbars will be overwritten every time Rhino loads.
Second, If you ever run the toolbarReset command, you must delete the configuration file placed in the %PROGRAMDATA% folder and start this process all over again.
Third, this configuration enforcement doesn’t respect the position of the toolbar.
hope this helps!