The council give a stadium safety cert, fire exits, markings, signs etc not whether the paths outside are safe for the public in a bit of frost. Everything is down to the match official.
As you say, it seems. An absolute nightmare to find out any info on the subject.
Normally it is under the advice of the police or weather authorities who fear for the safety of supporters outside the ground rather than the conditions inside. Sometimes it is the outside environment to the stadium that makes it unsafe due to road block or flood.
https://reflive.com/blog/abandoning-a-match/
Looks to me like nobody on here actually knows the protocol for this sort of scenario. One nicely written email or letter sent to the club will give you the definitive answer you seem to be seeking.
If outside factors like roads and pavements are a big issue than why would anyone bother getting under soil heating? I think they only come into play when there’s snow and ice about which afaik isn’t the case in Notts at the moment.
Setting off soon and the car half an hour ago said -3 so I don’t know what happens if the pitch starts to freeze over. No wind though so hopefully won’t feel too Baltic for those mental enough to be watching.