Just for information, the new ISP change happened today (From Sky to EE).
I must say I was extremely happy and the whole affair went without a hitch. Even Roon Arc reconfigured itself. It’s almost as though I have the same provider ( I obviously don’t). Many thanks to the support team, that offered many pearls of wisdom prior to the change.
I must admit, I was anticipating restoring backups or even reinstalling Roon Sever, but nothing of the sort… Just plain sailing. 
I’m happy that it went well for you.
However, with just a little thought beforehand, there is no reason that it should ever be any different - especially if you are using your own router - with the exception of ARC (without Tailscale) which can cause issues if moving from a service that does not use CG-NAT to one that does. Neither EE not Sky in the UK use CG-NAT so that is why you had no issues.
If using ISP supplied routers then Roon around the home should just work provided that you have not set your Roon Server (or any other Roon components) to use a static IP address.
ARC connectivity with port forwarding can cause issues if the router supplied by the ISP does not handle uPnP port forwarding requests well (or at least those issued by the Roon Server application) or, as suggested above, your new ISP is using CG-NAT. If you are using Tailscale, then even ARC should just work.
When changing ISP’s, there should never be any need to reinstall Roon Applications or restore databases. Provided no static IP addresses are being used, it should just start working although not necessarily straight away. If you do not power cycle your equipment, you may have to wait for DHCP leases issued by your previous router to expire (typically a few hours - maybe up to 12). Eventually, though, it should start working. If you are impatient, just restart or power cycle your equipment as appropriate.
Thanks, all very interesting. No static address used and I’m still confused about using Tailscale, as Roon Arc is working just about perfectly and has never let me down.
As you can guess, I’m not a tecky or a Roon expert, but had quite an anticipation about changing to a different ISP. Six years in now with Roon and never a hitch… It just works, however, your response and insight is much appreciated.