In the transmitter's gyro menu we assign a switch to control the gyro channel (channel 5).
When the switch is released we can set the tail gyro gain. As a starting point we use 50% gain (=50% deflection).
When we pull the switch for AttitudeControl, the channel moves to the opposite direction. Here we set -50% deflection, which sets the AttitudeControl gain to 50% as well.
Use the servo monitor to check that the gain channel changes direction when actuating the "rescue switch".