I don’t understand why you’d want to hide the transaction.
Without knowing the source or the motivation for the advice you received, I can’t say for sure why it was given. If you tag the tip of the current master branch then you can get back to that commit at any time, branch it into something else, etc… I don’t know why anyone would want to preserve “the branch”… especially since you are already renaming it. Branches are already almost only their names anyway.
What is the reason you wouldn’t just finish what you are doing on master-new (now poorly named), tag the head of master, then merge master-new into master?