This is a offer. We can add custom variables to Name... From registry or from another mod. Custom variables.

What do you mean?

In another mod i set for example
(im not minecraft dev for that i can be error)
registry.minecraftwindowtitle.newRegistry("newvariable", "newvalue")
And then i in config file writes
title = "New Variable {newvariable}"
And title is changes to 'New Variable newvalue'

You can already do that via TitleTokens.registerToken

Thanks.