Deprecation of 'Add Invalid Character' in version 2.7 of essentials

In Essentials there is a list of invalid characters which can be replaced during a migration.

Up to version 2.5 it was possible to add additional characters to the list.

In version 2.7 this is still a documented feature in the accompanying user manual but the option to add a character to the list is actually no longer present in the application.

I raised a ticket about this and i"ve been told that this was a 'Design Decision' and that the feature is now deprecated but could be restored by way of a 'Feature request' in a future release.

Does anyone know of a workaround (e.g. config file edit) so we could add invalid characters?