What happens if i change this? Total anhilation or business as usual?
The base URL in system settings? Definitely total annihilation 
It’s session cached so it’ll likely appear to keep working for a short time, then everything breaks. Some of the only reasons to change it would be when migrating from one domain to another (often done through the database at that point) or if adding https:// to an http:// base URL (which is always a good idea).
Maybe I won’t do that then. i used an IP address as it was only meant to be internal (IP is best for the special way DECD schools are setup) but people want to work from home now.
Well, in theory, if your IP address and domain name point to the same place, and your web server responds to both, then it should work if you change from IP address to domain name. That is why this field is editable, as occasionally it makes sense to change it (as Sandra mentioned above). If you try it, and it backfires, you can always change it back directly in the database, in the gibbonSetting table. Good luck!
Interesting. Which government is requiring this? Seems very specific? Just applies to schools, or generally?
i’ll probably just use a reverse proxy with URL modification when i add external access. it seems that reverse proxies are required by governing body for this kind of thing.
Its an SA DECD thing. They are security mad, we couldn’t use Office 365 until Microsoft put a data center in South Australia that hosted all our services. And after that the principal must sign a 20 page risk assessment and letters go home to parents to opt out of access. The required risk assessment for google apps for education is 27 pages and about 10 pages to get a website placed on the proxy bypass by url list.