How to disable air recirculation permanently?

Are you using the air conditioning (AC) a lot? That can contribute to smells: the AC radiator within the vent system is very cold, so moisture in the air tends to collect on it (like a cold glass of water). This moisture can remain for along time, get moldy/smelly.

 

maybe with tech stream, ask a dealer

 

If you’ve selected Eco drive mode, as the Owner’s Manual (PDF) describes on page 244, “Outside/recirculated air mode may automatically switch depending on the temperature setting or the inside temperature.” To prevent this, as @bisco kindly suggests, a Toyota Techstream diagnostic system can be used to change a setting, mentioned on page 525 of the Owner’s Manual. The Repair Manual (more info) says the actual name of the setting is “ECO MODE Cancel,” but I don’t think it disables Eco mode in general; it just means the air conditioner won’t change its behavior when Eco mode is selected.

Later Prius c models also have a setting called “Outside Air Mode Auto Switch Function,” which automatically selects fresh-air mode when the car is parked. If that setting exists on your car, it should be enabled by default.

 

Would you know: would the revision be maintained if there was a 12 volt battery disconnect?

 

BAD idea.
Unless you already HAVE a moldy smell, sucking in outside air will result in the AC evaporator accumulating more water not less........and pretty much exactly the same amount will be left after you shut it off.
There is a fatal flaw in your theory.

 

If it stinks that simply means the evap coil box under the dash is getting funky.
Clean it!

Go on Amazon and buy 2 cans of Kool It. Comes with the connector hose to connect to the drip hose under the car. You inject the whole can of cleaner up the hose goes up as foam then drains back out that hose as liquid.

makes the ac smell nice again and keeps e box clean and the drain hose clear. Dealer charges $150 for this service if you prefer that method.