> I suspect that specifically car / aircraft / spacecraft computers receive regular updates, and these updates change the smallest part they can.

In the space I am very familiar with, automotive, this is not true for code changes to most automotive control units; the "application software" code for each control unit is treated as a single entity and built, supplied, and modified at this level of granularity. Infotainment and digital cockpit is the only major exception, but even then, only for the "unsafe" part (Linux/QNX/Windows); the "safe" part is usually a single-image single-application running on a safety processor alongside.

Sometimes personalization/vehicle-specific "data sets" or calibration _data_ (ie ECU tunes) can be updated without updating the application software, but the application software for each unit is generally treated as a large unified firmware blob. For example in every ECU I am aware of, modifying the application software logic (which is usually modeled in something like like Simulink/ASCET, not code directly) triggers a full code regeneration, recompilation, and generates a complete new firmware image with an updated Application Software version. There isn't any notion of shipping a new "turbocharger control" code module, or a new "diagnostics" code module, or whatever, even if they are constructed at this granularity in the code generation suite or run at this task granularity in the RTOS.