How to use different text customizations with multiple Custom Databases?

I’m trying to use the new Organizations feature to present two different brands with the New Universal Login. This is working quite well.

Each brand has it’s own custom Database authentication, in addition to Social authentication options. For one brand, it accepts an Email address and password. For the other one, it accepts a numeric User ID and password.

The problem I have encountered is that the display text for the Email address and the User ID is called “Email” by default, and although I can change the label using the custom text APIs), I can’t have a different value per Database.

It seems to me that this should be determined at the Database level, not the Tenancy level.

I could create additional Tenants, but we have plans to merge the brands in the future, and I’d prefer to avoid migrating users.

Are there any other options to display the right label for each of these different Databases within a single Tenant?