I'd just consider this a templating/language-string editing task. That's because if we go down the route of allowing config options for customising individual optional snippets of text in places we'd be adding like 50 new options. However, I do think there's an alternate way of handling this which is cleaner and more of a checkbox thing, I'll add a new issue for it.

Sorry that's not what I meant. What I meant is one option to set an optional support string that would display on all errors. Sorry for confusion.

Yes, I just mean as a policy, if we allow config-based setting strings of text for particular UI cases we pick out (there could be many just as worthy as this one), people would want us to allow it settable everywhere. I don't think that road of thinking works for us.

I've just opened #2652 which takes an approach of automating the messaging, and the only config requirement on the user would be a single checkbox.

That means there's less config noise, as sensible default approach works out of the box, integrated with the ticket system. If they really did want to customise further then they could edit the language string and/or templates.