No. 3 transmitter id code cannot be reprogrammed
Location indexMazda 6 Service Manual: Manual Shift Mode
The manual shift mode gives you the feel of driving a manual transaxle vehicle
by allowing you to operate the selector lever manually. This allows you to control
engine rpm and torque to the drive wheels much like a manual transaxle when more
control is desired.
To change to manual shift mode ...
Mazda 6 Service Manual: Cargo compartment light switch inspection
1. Remove the liftgate lower trim. (See LIFTGATE LOWER TRIM
REMOVAL/INSTALLATION)
2. Disconnect the cargo compartment light switch connector.
3. Inspect for continuity between the cargo compartment light switch
terminals using an ohmmeter.
If not as specified, replace the liftgate lock.
...