No. 3 transmitter id code cannot be reprogrammed
Location indexMazda 6 Service Manual: Dual proportioning valve replacement (without abs)
1. Remove in the order indicated in the table.
2. Install in the reverse order of removal.
Dual Proportioning Valve Installation Note
Install the dual proportioning valve so that the R mark faces the left side
of the vehicle.
...
Mazda 6 Service Manual: Opening the Hood
1. With the vehicle parked, pull the release handle to unlock the hood.
2. Insert your hand into the hood opening, slide the latch lever to the right,
and lift up the hood.
NOTE
The lever is located a little to the left of center when facing the vehicle.
3. Grasp the support rod in the pad ...