It's pretty unusual for any item to offer the ability to offer a firmware downgrade. By it's very nature, a firmware update fixes problems and software errors which were previously not identified. They invariably improve performance in one way or another, be that power, efficiency, smoothness, longevity. To enable you to go back is to re-introduce known problems, so logically, would invalidate a warranty ?
Imagine in it's simplest form :
Hi, we've updated the firmware to stop it breaking.
Well, I changed it back and it broke and now I want a new one.
If you look at Tesla for an example. The older Model 's' cars have a reduced range at present as Tesla has locked down the voltage range to temporarily stop a reduction in battery health. They've not done this to make the cars crap for people. They've done it whilst they try to work out a way to make the batteries last longer, so rather than have them degrading whilst they work on it and then have a battery which is too far gone to be worth doing anything with, they've done it so when they do have a solution, you'll have more range and a battery which will last longer.
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