That gold code could be received and decoded anywhere on the network. If power islanding occurs, embedded generation will detect the loss of the gold code (since they are no longer connected to the generator injecting the code), and cease supply.
The only disadvantage is it introduces a security vulnerability by design: Anyone could transmit the gold code from their house, effectively disabling islanding protection in their neighbourhood. If power islanding were to occur, and if there was sufficient embedded generation to keep a stable power island, grid hardware could be destroyed through overvoltage, overheating, and circuits closing without frequency synchronisation. I think it's a worthwhile tradeoff though - damage will be localized and minimal, and a very unusual set of circumstances have to happen outside the attackers control for the attack to do damage.
Sometimes I think that a DC grid would be better. Issues like frequency synchronization wouldn’t exist.
There is currently no way to control the frequency or phase of the island.
ROCOF works well to keep things safe when only a small percentage of the grid demand is met by residential solar/powerwalls.
As soon as any significant proportion is residential solar (and thats already the case in some countries at some times of day) it acts as a cascading failure mechanism. As soon as any failure occurs, embedded generation sees a rapidly decreasing frequency, and rather that increase supply as traditional generators would be instructed to do to stabilise the grid, ROCOF protection requires they cease supply, making the issue far worse.
Within a fraction of a second, all embedded generation will disconnect, likely causing a near total blackout nationwide. Since system frequency that ROCOF measures is nationwide, failures won't be local to one geographic area.
I suspect these rules were made when people thought "consumers feeding energy back into the grid will never be more than 0.1% of the total - we'll always have enough spinning reserve to make up for that". Thats no longer the case, and unless the ROCOF limits are changed, and the majority of home solar/wind/powerwalls get a firmware update, expect a few very large blackouts.