I’ve had this problem for quite some time so happy to see a fix may occur. Thanks!
@julian the inherited themes didn't work before, but is it possible that now you've made this commit:
There is scope for the template inheritance to be used there instead of the hardcoded rule 'nodebb-theme-vanilla/templates'?
Right now I'm maintaining an entire theme that's a fork of lavender just so I can restyle one or two pages.