Pixhawk bootloader

Hey folks, I’ve got a partially dead Pixhawk that I’d like to revive.
The I/O part blinks happily but the FMU LDO regulator was dead. I soldered it out and lacking direct replacement at hand I hacked in a 3.3V switching power supply.
Once I connect it to USB I get a “USB device not recognized” message, red light on the RGB led and serious heat from the F4 microcontroller.
I’m contemplating dropping a $13 replacement STM32 instead of writing the FC off. Will I get into serious trouble re-writing a proper Pixhawk bootloader ?