I was looking at the HubSpot pages settings where you have the 'Branding' and 'Personalisations' tab.
I think it would be awesome if it's possible to create custom properties by domain level so these could be used inside the website templates.
At the 'Personalisations' tab underneath the 'Company property defaults' there is an option to add 'Company Domain Name'. This is only possible for the complete portal and not by domain.
My thoughts are, letting the user add custom properties by domain at the 'Branding' section, since it's a part of the website. Therefor you can change it based per domain.