Those modifications seem unlikely, You can't easily reinforce pillars in a car and they are designed to support the full weight of the car in a roll-over situation so a few 10s of kgs of equipment on the roof make little difference. Similarly, a typical alternator is rated to 2kW so far above the required power of a few LIDAR, camera and computing devices. Having said that, early vehicles did have heavy duty alternators installed (although they may have confused these with heavy duty inverters which are needed) and modified suspension components [1]
Fwiw, direct fit high-amp alternators are available for most cars. And they are in the same ballpark of ~200 amps, and high output at idle as a "fire truck alternator".
So it's a fairly cheap modification just to swap out the stock alternator. ~$500 or less.
I think it should "just work". The added load would drive voltage down, so the inputs the ECU gets continue to send the right message. So long as the alternator has enough capacity to meet the demand...
Yeah if a manufacturer wanted to hold off on drawing a higher load to recharge the battery until after the car was warmed up they would just do that by lowering the setpoint. If you try and draw higher current from it it would still meet that lower setpoint.
[1] https://pub-tools-public-publication-data.storage.googleapis...