For starters your problem could be just a wiring problem due to the age of the wiring. Start with checking earths. You will have to be patient and systematic. About 13 earths go to the connecting block under the front of the battery.
The BCM is not difficult to remove. you just have to unplug everything and remove the bolts.
But unless it can be repaired you cannot easily swap it for another BCM. The eeprom inside will have to be unsoldered and swapped over to the identical replacement or you will need an ECU BCM keys and locks as a set from a single used car. The used set costs about 100 pounds