I am wondering if it is possible and safe to add a second extruder to my Anet A8 without changing the main board. I was thinking splitting my Z motor wires to free up the Z2 axis motor connector on the main board, using this connector for the second extruder motor. Is this possible? If so, how would i configure Marlin to use those extruder pins Can I overload the board by using two motor on the same connector?
That is not possible without changing to a different printer main board. The Anet A8 board has 4 integrated (A4988) stepper drivers, one for X, one for Y, one for Z and one for E (extruder 0).
Both Z steppers are controlled by a single stepper driver (they are wired in parallel to the single Z stepper driver), there is nothing to free up nor is there to configure in Marlin without replacing the main board.