All settings are stored as a model memory in the TX.
Based on this programming/switch position/stick postion, the TX computes an appropriate command for each channel and mashes it all together and transmits a representative signal into the atmosphere on a specific carrier frequency.

ANY RX, tuned appropriately to that frequency will pick up the signal and attempt to decode it. If all is compatible, the RX will translate the signal into independant channel commands and send it to "whatever" is connected to that channel socket whether it be servos or gyros or other things. The device (servos,gyros,etc) must be capable of doing something with this "servo" signal. Unfortunately, the servos are dumb, they will respond to anything sent to them from the RX ... whether it's right or wrong (ie you select the wrong model in the TX, RF interfence, someone with a TX on the same frequency, etc).

So, the servo will always move to where it is commanded to move because you already have the TX turned on before the heli is turned on. And when the heli/RX/servos/gyro is powered on ... they will be sent a command that the TX has already figured out. So if you swap to a newer improved RX, as long as it's compatible with your TX and it's transmitting mode (ie PPM or PCM) them you will be OK.

That's why the hobby is called RADIO CONTROL.