I just played with this a little. In a stand-alone TCC console, Option\CommandLine\EditMode ... Insert\Overstrike ... Apply\OK ... the new setting is applied immediately. If I do the same in a TCMD-tabbed TCC, the change is not applied to the current tabbed TCC instance (WAD?) but is in effect for newly-created tabs and when TCMD is restarted. So it might help to make the "Insert" setting and restart TCMD.