After searching this didn’t seem possible but I’ll ask anyway.
I’m currently finishing off with somebody an integration so that Ghost can be used as the SSO Provider for Discourse, connecting the two membership systems together. I’ve duplicated the Ghost footer in Discourse, which over in Ghost can be changed based on whether the user is signed in or not via usage of something like the following:
{{#if @member}}
Welcome back!
{{else}}
Join
{{/if}}
Is something like this possible in the Customize → Theme → Edit CSS/HTML → Footer section of Discourse?