"a lot", not really, just enough to make my device work properly

I shouldn't even have to fix their sh*t
The reboot issues many people have can be related to logs which are stored in RAM and can rapidly grow to few MB depending on the car headunit. The device only has 64MB of RAM and can start killing processes if not enough RAM is available (and finally reboot). They removed the way to disable logs from 192.168.50.2 since August (I don't remember exactly, but recently). The custom firmware completely disable logs so all the RAM is used for running processes not saving logs.
Concerning the rest I can't help you, as told earlier, all interesting things (Carplay things) are packed in binaries and we don't have the source code.