I've a few accounts that are no more active, and I don't want to remove them in order to not smash the operations done on that account.
Having such accounts in the operations editor menu is annoying and led me to some error while inserting an operation.
Is there a way to hide the account (mark it inactive) keeping it in the accounts list but removing it from the operation editor?

Yes, you just have to close it.
See contextual menu.

Thanks, but in my version (1.9 beta 3) I don't have a close operation in the context menu. However I've got a column with a red X that does the trick.