Well, here are a few of my thoughts on the Passlock system after reading the factory manual. First, I don't see the point of tying the yellow wire to ground using resistors. The system does not measure resistance, it works on voltage. Each ignition lock has a different code voltage based on the resistors in the lock. This changes the voltage sent along the yellow sense wire. Tying that wire to the black wire with resistors seems to be taken from some websites that deal with shutting off the Passlock system when installing an aftermarket starter or alarm. However, the key piece of information left out is that after measuring the resistance, the resistance is then programmed into an electronics box that is wired into the vehicle. Since this box gets 5V power from somewhere else in the vehicle, it doesn't tap into the reference voltage wire going to the switch. So, you'll probably get the same result of you just wire the yellow wire to the back wire. Or, you could use any resistor since you are going to "relearn" the system anyway.
In my opinion, you could achieve a voltage drop to fool the system by placing one or two diodes in series from the hot wire (or any 5 V wire) to the black wire. Typical diodes drop 0.7 V so this gives a 1.4 V drop - enough to fool the BCM after it is relearned. Make sure the diodes are placed in the right orientation. And note, you are not using this as a diode, just as a voltage dropping device. This is probably easiest to do by the BCM (located under the dash on the passenger side of the vehicle). Just my thoughts.
Finally, the relearn sequence (according to the factory service manual) is:
1. Turn the key all the way to start and then let it come back and stop at the run position. This assumes the car won't start.
2. Leave the key in this position until the Theft light stops flashing (about 10 mins.).
3. After the light stops flashing, turn key off for a few seconds and then you can start the vehicle.
I have found that sometimes the Theft light comes on after doing this procedure while driving and then goes out after a few minutes.
One final note, I checked the BCM on my 98 Malibu and found corrosion on some of the pins that corresponded to the Passlock system. I cleaned them off and recrimped these for a better connection and have not had a problem yet, but it has only been a couple of weeks.
Good luck everyone. Hope my ramblings are helpful to someone. I just thought some of the misinformation in the string might steer someone to the wrong solution.