Firmware downgrade possible?

[baggins]

Hi,

At the moment I have two LM4 with a read-only SD card.
In the near future I will replace them with the usual procedure.

At the moment they both use firmware 20160714. The reason for this is that during the upgrade to that version there were some issues with a third party library which is used for the ventilation system.
The developer of this library cannot guarantee that there will be no problems with this library during an upgrade and on top of that he is very difficult to get hold of.

Now this is what I would attempt to do:

• transfer the image of the old SD card to a new one
  
• verify that everything is working as normal (which should be the case)
  
• upgrade to firmware version 20200720 and see if there are any problems
  
• if there are no problems I can the keep that SD card in operation
  
• should problems show up I would replace that SD card with another one with the image of the old SD card
  

The question thus is: does upgrading the firmware make changes not only to the SD card but also to some other part of the system because in that case I would not be able to go back to the old firmware...

Thanks for your advice.