@Kool ******
Where do you read there is no need the money stays in your account?
It is stated as visa requirement, and not as a requirement at moment of application only.
A lot of people here seem to think requirements are only at moment of approval, which of course does not make any sense.
Why should they want you to have 500K at the moment you apply for the visa and not anymore when you actually visit the country? What would be the logic behind that.
It is not a loophole, the 500K has to stay at the account, but the chance it will be checked is very low, and that might make your idea work.
But even when it works, there is no guarantee you will not be checked somewhere in the 5 years, and grandfthered only means that old rules are respected when new rules become active, so that has nothing to do at all with this situation.
The granted visa is only valid as long as you comply with the visa requirements.