Well that's kinda what we would do if we just wanted to replace old issues with new issues. But we wouldn't issue the new treasuries for the purpose of buying back the old ones. What we would "functionally" do is buy back all the Treasuries we wanted to buy using money all ready printed, spent into the economy for goods and services and then returned to the Government when we issued the Treasuries in the first place. If we were to but back all the Treasuries, which we won't do, the total money in the private sector economy wouldn't change but it would all be in the form of bank reserves and none of it in the form of Treasuries.
Selling Treasuries in the first place returns to the Government side of the ledger new money printed to cover deficit spending into the private sector. The fed, at any time, has the option of just reversing that swap of treasuries for bank reserves to the extent it sees fit. That's what the fed routinely does to control the ration of private sector outside money in the form of bank reserves to that in the form of Treasuries.
What's instructive is to contrast the net result of printing, deficit spending and Treasury auctioning (in that order) with Treasury auctioning and spending borrowed money (which we don't do). We print all the money we need to cover our deficits, we don't borrow. We do issue Treasuries in principal amounts equaling our deficits, but it is for purposes other than borrowing.