I think you misunderstand what "electronic money" is - moving electronic money around isn't simply a matter of sending the right "codes" - it is ultimately about asking the central bank of that currency to move money around.
Sure you can open up excel and write in it "I have \$100" but that isn't USD, much as writing \$100 on a piece of paper doesn't make it a \$100 bill.
In order to lend you dollars I actually have to have some dollars to lend you. That means I need a reserve account with one of the 12 Federal Reserve banks. There are no electronic USD that are not ultimately in a Federal Reserve Account.
The "ultimately" in that sentence is there because banks can (and do) form hierarchies. Only the largest ("Tier 1" banks, sometimes called "clearing banks") actually have a reserve account with the central bank in a given currency. Other, Tier 2, banks will simple hold accounts with Tier 1 banks. Smaller local banks may even be Tier 3. When it comes to foreign currency dealing, you could be even further down the chain (i.e. a small bank in Australia may be Tier 4 for USD)
Because of this hierarchy a certain amount of electronic banking can be done without moving reserves. A transfer only needs to progress up the hierarchy until it gets to a common bank between the two customers.
So for example:
A payment between two accounts at the same bank, can be done on that bank's systems.
A payment from an account at a Tier 2 bank, to a different Tier 2 bank might be done using a shared Tier 1 bank. The Tier 2 bank's are "customers" of the Tier 1 bank, and so the Tier 1 bank can do the transaction on their system.
A payment between customers that ultimately fall under two different Tier 1 banks must be done by at a Federal Reserve bank.
The US adds an extra complication, because there are 12 Fed Reserve banks - if two Tier 1 banks don't bank with the same Fed Branch, then the Fed Reserve System also has to go "one step higher" and the New York Fed acts as the very top bank: "How do reserves move between the 12 federal reserve banks?" explores exactly how that is done.
So the problem in your scheme is you couldn't get your central bank "into" this pyramid of banks.
Your central bank's computer can show $1tr on screen but the only way to transfer to another bank, would be to instruct YOUR Fed bank to take money out of YOUR fed reserve account and put it into the other bank's account. Your central bank can't make reserve dollars.
Aside: An alternative way of looking at this, for those familiar with how BitCoins work, is to note that the important feature of electronic money is to prevent double spending. BitCoin does this with the BlockChain; the USD equivalent of the block-chain is held on the Fed Reserve computers. You can't just declare yourself to have billions of bitcoins - to spend them you have to get your transactions onto the BlockChain. With electronic USD you have to get your transactions onto the Fed ledger. Only the Fed has a copy of this and their say is final. There would be no way for your central bank to change the Fed ledgers.