Resetting UNO testnet3 from the gensis block wouldn't even be a fork... it would just be a new coin, testnet4 (ProtaniumII or UnobtaniumJR).
If it was so easy to evaporate an entire network, someone would have come along by now and done it to Bitcoin.
Show me how, and lets go test your theory on unattainium.
No, resetting the testnet literally just starts the blockchain over from the beginning. It just wipes it. It's no new coin, it's just restarting the testnet. It's plain and simple. Only way you are keeping any coins is forking it and running off on another chain *before* it gets wiped.
They have done it with Bitcoin, several times. Hence, testnet3.
If you want to know how, just look into using the Bitcoin testnet and see how the testnet is used. Read around, Bitcoin's testnet is not allowed to be monetized for all these reasons and so it can be wiped, stress tested, abused, hacked on at any time.
I was only mentioning this to clarify to you because it was apparent that you initially thought you could keep many chains and keep the coins. It does not work that way. It's just reset and it's gone, or fork the coin before hand and turn it into another coin.
A fork
is a new coin. (The one time I find myself agreeing with lukejr....ughh)