People are always praising that fanfic for some reason so I tried reading it a while back. If it's the one I'm thinking of then hard disagree, the protagonist is a self-insert Mary Sue clearly written by a kid who thinks they're the smartest person alive. One part that still sticks in my mind years later is their fundamental misunderstanding of how fiat currency works, it was some ridiculous get-rich-quick scheme like melting down wizard currency into pure gold to sell to non-wizard community then using that money to buy silver which they'd trade up to magic society gold coins. It was some years ago so I may be misremembering the details, but there should be a ton of issues that immediately jump out to you there.
I trudged through and got as far as the first meeting with Malfoy where the author realized they were being too friendly with each other, but since Malfoy is supposed to be a bad guy they decided he should randomly blurt out something about how he wants to rape some girl.
Maybe it's just because I don't have the context of other bad fanfics, but that's a solid 0/10 from me.
If the coins are 100% gold or copper then you're in one of two scenarios: the value of the coin is the scrap metal value, in which case swapping between gold and copper makes little difference; or, the mint buys your scrap gold and converts it in-house, pocketing the difference. A mint has no reason to convert your gold to significantly higher value coins for you, that only loses them their economic and political power in the form of currency control.
The only way it would work is if you specifically build a world where everyone else is incredibly stupid just to make yourself seem smart.