How do I "disconnect" an account though saving it's last update?

My credit union made a significant update . It included a new way of labeling deposit transactions. I entered the hospital for heart surgery during this time and didn't actually know what was happening. Now all deposits are credited to a new account that was created by the institution while I've been showing them as entered the old way. Further I was entering the checks the old way while the institution was posting them to the account they created. The solution is pretty simple though tedious. However, how do I terminate the linkage between the old account and the "bank?' I need to keep the file but want it to become inactive I guess is the way to say it.