If the current club was able to get promotion to the National South league, the ground would be subject to football Association Grade B grading http://www.thefa.com/get-involved/player/ground-grading which would only need minor upgrades to the ground, and plenty of that has been undertaken (for example turnstile lighting has been upgraded in 2021).
There must be at least 6 spectator entrances to control the ingress of spectators. These must be controlled by fully operational turnstiles of the revolving type and must be suitably housed and lit. Adequate protection and security for the turnstile operator must be incorporated. These entrances should be placed in appropriate positions around the boundary of the ground and take into account the requirements of segregation.
Clubs must be able to demonstrate that visiting supporters can be segregated when necessary.
When segregation is in operation, there must be adequate toilet facilities and refreshment facilities in each segregated area in addition to the appropriate means of egress and exit.
All of these seem readily achievable, and segregation was proven to work when AFC Wimbledon visited. Maybe only minor things might change – something like the naming of the ground (the “Neil Cugley Stadium”? He’s represented the old Folkestone FC club with distinction and managed Folkestone Invicta for over 20 years)
The requirements of modern football all seem to be currently satisfied: Without the prospect of elevation to an even higher league, it seems that the Cheriton Road football ground is likely to stay as it is for the foreseeable future. Maybe that’s a good thing as many visitors and locals alike seem to like it that way.