I just purchased a 2019 Nissan Versa Note SV. The SV had a package available to upgrade the unit to have Apple CarPlay and AndriodAuto functionality, unfortunately, as Nissan is discontinuing this model, there are zero Notes with that package available in the country left.

However, when I plugged my iPhone into the USB to stream audio with the old iPod interface system the vehicle does have, the iPhone prompted me to approve the vehicle for CarPlay permissions and is now listed in the CarPlay section in settings. I am assuming that means Nissan has the same head units and screens in both variants, but simply have the ability, on a software level, to turn the functionality on and off for individual cars as they were coming down the line. If that is the case, would this be something that could also be overridden somehow so I can use CarPlay?

I'm not sure exactly how Apple decides to prompt for carplay permissions. It could happen anytime you connect, or it might be based on certain conditions upon connection.

It's certainly possible that Nissan is using the same headunit with different firmware configurations (or even the same configuration with different features enabled). It would make sense for support, licensing, etc.

One possibility for them dropping it would be licensing for CarPlay. I imagine Apple charges heavily for CarPlay compatibility claims, so even if the support is there in firmware, disabling it could save costs by not requiring licensing since there's no associated branding. If you have a way to interface with the headunit, you might be able to dig through and find more, but these types of units are generally pretty nonstandard and not easy to dig into, even for pros--though they do tend to use Linux, which at least guarantees certain file system and structure compatibilities.

Another, possibly less appealing option, might be a CarPlay compatible aftermarket headunit. There was certainly a decent stretch of time during which CarPlay was very costly on aftermarket units, but these days it's not hard to find a mid-range double-DIN unit with decent display for under $200.