I suspect Tesla can define geofenced regions, where each region has its own weights. Drive into England? Car downloads and starts running with England weights. In New York City proper? The weights curated to that area are installed.
I suspect there are a LOT of weights, but they are just floating point values, so downloading them via cellular connection wouldn’t take too long. The car could even possibly cache onboard any regions within 100 miles. When you enter a region, the new weights are pushed to the secondary processing unit. When ready, car control switches to that processor while everything is loaded into the primary unit. So the switch can be done while driving, with only a loss of let’s say a second of compute redundancy.
Edit: Ninja’d by a Canadian