Ahh! The routing idea probably can work for me here. We’ll be swapping ISPs soon, and the new one will be the one that I will be able to let change without having to deal with using the secondary WAN as my actual WAN for hosting things on.
I’ve added comments here: Update dns.rst by Dibins · Pull Request #1105 · vyos/vyos-documentation · GitHub (hopefully that link works). I think I explained it well, but please feel free to provide any feedback!