Typically, no, receivers will not need re-binding after a MULTI-Module firmware update.
Occasionally there are changes to protocols which will make re-binding necessary. If this is the case, this will be clearly stated in the new firmware version release notes.
Typically, no, it is not necessary.
AETR is the default channel order on most MULTI-Modules, but any channel order can be used and none is better than another; it is just a preference.
The main factor is whether or not you have existing models in your radio.
Stick with the default (AETR), it's just easier.
It is not necessary to change the MULTI-Module channel order, no matter what models or receivers you are going to use
Before you create any models you should configure your radio's default channel order to match the channel order of your MULTI-Module (AETR is the default)
As you create new models they will work correctly, no matter what channel order the protocol expects as the MULTI-Module will automatically translate the channel order from AETR into whatever the model needs (e.g. into TAER for DSM)
If you still want to change:
Pick your preferred order
Pre-compiled firmware is available for AETR, TAER, and RETA; for other orders you must compile the firmware yourself
Update the MULTI-Module firmware
Set your radio's Default Channel Order
Update any existing models
If you have configured a number of models with a channel order other than AETR (and you do not want to reconfigure them) then it probably makes sense to change the MULTI-Module's channel order to match your existing models / radio default.
It is usually enough to obtain a single fine tune value once per protocol or receiver type. Variation of +/- 5 between receivers is OK.
You may want to check the fine tune values between different types of receivers using the same protocol, e.g. S6R vs. X8R.
That said, fine tuning each receiver cannot do any harm if you are concerned about it.
Many different models are supported by the existing 300+ protocol variations. It is not uncommon for a new manufacturer or model to use an existing protocol.
To find if a particular model is supported:
Use the Search function to search the documentation for protocols which may mention your model
Ask on the RC Groups forum
If you post on the forum you will be asked for details of the model, and may be asked for close-up photos of the inside of the transmitter (to identify the RF components).
Once the RF components are known you can try all the existing protocols which use that component.
If you have a model which is not supported, you can ask for support in two ways:
At a minimum, you will need to:
Provide high-quality close-up photos of the inside of the transmitter and the receiver
Be able to compile the MULTI-Module firmware from source and update your module
You will also need to provide protocol data in (at least) one of these ways:
Dump the protocol over the air using an external MULTI-Module connected to a computer (only works for some protocols), or
Connect a USB logic analyzer to the model and provide 'dumps', or
Ship the model (TX and RX) to the developers
The time and effort involved will depend on the protocol.