You don't need a flag convar, just set it to default the Admin Chat flag and just rely on Sourcemod's Command overrides to do the rest. This saves you from having a registered convar and from jerry-rigging the RegAdminCmd before OnConfigsExecuted. Pretty sure since you set the command flag before OnConfigsExecuted there's no way of changing it via the config anyways it will always be the default value.
Yeah actually you have a lot of logic that isn't needed, you retrieve the convar as an int then convert it to string...
and you do this logic twice if the flag convar turns out to be blank:
HTM = CreateHudSynchronizer();