This is a question for an expert in the South Korean legal system.

If a US state governor OTOH tried such a move, I'd expect litigation.

I guess many thought sovereign gold reserves were also impossible to sieze and yet...

I'm always confused by this type of perspective. It's like asking "how is it possible to lie" or "how is it possible to say xyz"

What laws of physics prevent people from reneging on financial agreements? It happens a million times a day. It's one of the most believable human interactions. What part of it doesn't feel possible to you?

The part where there are no checks and balances. No court to issue a decision saying it had to be honored.