Actually, good luck with that one. Honestly, I've spent years working on the internals of these cars now, and as far as I know I'm probably the only person outside of Tesla's engineering team that has broken any of the proprietary logging format used by the gateway (a couple of others have gotten some of the basics of the structure down, but AFAIK no one else has worked out what any of the data means). Next, faking these logs would be extremely difficult, and they were obviously designed with this in mind. (Kudos, Tesla) I'm not going to get into those details, but suffice it to say faking the log would probably require physical access to the car to do in any timely fashion (physical removal of the logging card from the MCU). Second, you'd need to fake a lot more than accelerator pedal position, since the entire situation can be reconstructed from the logs. Pedal position is one of hundreds of variables, including accelerometer data, wheel speeds, even the approximate weight of the driver and passenger in the case of newer cars. Any break in the logs would be immediately obvious, so trying to splice in something wouldn't work due to the way things are logged.
I'm actually sitting here thinking about how I would fake a Tesla log, if I were so inclined... and I don't think even I could do it convincingly. Tooting my own horn here a bit, but I think this would put it in the realm of the impossible for most other people.
I've considered this scenario as well... and actually attempted to do a proof-of-concept of this type of apocalyptic event. It's also pretty much impossible based on the way the system is designed. Specifically the part that hung me up was that, accelerator input and torque control is verified and crosschecked by multiple systems, including two FPGAs. Not sure how many here have worked with FPGAs, but even with the synthesized binaries it would take years of work to even begin to reverse engineer the "code" (gate layout). You basically would have to get your hands on the FPGA source to do so. Even then, you've got to hack several other modules to ignore their crosschecks. And really, they've stashed a lot of safety crosschecks in things. It truly is impressive.
Best case, you can get the car to accelerate at a few MPH per second autonomously with a bunch of hacks. Basically using the same functions Tesla is using for their planned FSD stuff. But that stuff isn't going to be doing pedal-to-the-floor type launches. We'll be lucky if it does 0-60 in 15-20 seconds.
Long story short, I wasn't able to realize my dream of programming the car to do a 1/4 mile run with no driver... at least it won't happen without a physical accelerator pedal connection hack.
