There are a million ways to skin this cat
FWIW, my reproductions stay scabbarded and have occasionally been wiped with a cloth damp with light oil or silicon spray. Of the dozens of antiques here on my watch, most are clean and dry after working with them. I dust them from time to time.
One sword I bought from a dealer that uses paste wax for both cleaning and preserving , preserved active rust on the blade, the pits getting deeper (it was much brighter once all that had been removed). Ren Wax gets good marks, as well as any protective (just make sure it is clean and dry first). I dug out a fifty year old can of liquid silicon glaze I have been using on various things and plan to do some of my swords when I have them out for a show this month. Cans of silicon spray are cheap. Spray on, wipe with paper towels. Treat cloths and you basically have gun cloths. Any automotive wax Ballistol, Break Free and any number of other products work fine. I by bottles of Whal hair clipper oil, which is fine mineral oil. Honing oil, similar and someone just gifted me some. If a blade is displayed open, oil will attract dust and settle, wicking moisture. Vegetable oils do get rancid in time and are thick. In this age, there is little need for them aside from camellia oil, which is proper for Japanese blades and used by many woodworkers for their tools.
In the end, it really isn't brain surgery. When stuff rusts, I generally remove it unless leaving it purposefully. Here is a war hammer getting prettier all the time
That was the first go before more oil and rubbing then getting browner by the year.
Anyone that uses knives that discolor over time note the patina. Usually just getting grayer if cleaned after use.
As mentioned, my repro civil war sword lives scabbarded and pretty clean and dry after handling at shows and cutting. It does pick up rust from peoples oily acidic fingers. I don't worry about it (I just let it patina and blend it in scrubbing with Scotch brites or copper scrubbers).
My sword from Blockade Runner before some scabbard speckling. and now darker brass from handling.
I have brought back a lot of old leather with Pecards Antique formula but many have their own favorites. Leather as old as the mid 1700s has responded favorably.
If you want to make the blade look old, there are lots of recipes. Mustard, for instance. For a smooth patina, just keep rubbing with fine abrasives, cloths and oil. You are in charge. Lots of food acids out there but even just humid air will do it. Bleach is just nasty stuff for blades.
Cheers
GC