The CMIzapper turned up a few days ago, installed it straight away and having been running the laptop for a while to see if there's any issues. So far so good.
The GPU was definitely causing issues even at the boot stage as the GRUB bootloader wouldn't even show up running the AMD GPU, now GRUB shows up at boot.
The previous workaround in software disabling the GPU by telling linux to not load any AMD drivers was clearly not enough, as the system was recognising the system and the GPU was causing the whole system to freeze randomly. As you can see now the GPU isn't even detected by the system. Also, battery life has drastically increased, the GPU must have been absolutely chewing power (less than 1 hour battery life before).
Keyboard and backlight dimming still work, not sure if the mod is needed for linux, but I did it anyways. The display doesn't auto dim down anymore after ~5mins, though I'm not sure if that's hardware or software based, as all the keyboard brightness controls work as intended.
So far a pretty successful revamp of this laptop.