bkubicek/Marlin — comment on commit ad4ae7c7f8e5c44e36e34de83387e76cbbe658fb
File:  line 0
By lampmaker:

I wouldn't do it like this. the EEPROM_writeanything needs to know the type/size of the variable to be written.
Why not just keep Kp,Ki,Kd in the code, even if PID is disabled? The at least the EEPROM reads&writes fine and is compatible.

Alternatively, it's perhaps best to switch between PID and simple on/off using an M code

e.g
M302: use PID
M303: use on/off