Regarding the INS/OVR mode, it always uses the last-used mode.
What SAPGUI does is to store in the registry, which mode was used in the previous session.
If key HKEY_CURRENT_USER\Software\SAP\SAPGUI Front\SAP Frontend
Server\Customize\Edit.InsertMode is set to 1, you have the INS mode; 0
is OVR mode.
So if the customer wants to start SAPGUI each time in one of that modes,
he can write e.g. a small script, which sets this registry key.
Hope this can help.
Regards,
Jude