Probably not, most devices have the first stage boot loader on read only memory that is locked using an e-fuse. You would need to physically modify the device to change it.
FWIW, I had an older Fire tablet that I had loaded Android onto and it wasn’t great. It would crash randomly and the battery life was awful. These days I have a newer Fire tablet. It’s a few years old now but I still use it all the time for reading e-books from the library, and I have a few Android apps loaded onto it that I use for working on my car and they all work fine. In other words, there’s not really any reason to reflash them, the stock OS is fine.
FWIW, I had an older Fire tablet that I had loaded Android onto and it wasn’t great. It would crash randomly and the battery life was awful. These days I have a newer Fire tablet. It’s a few years old now but I still use it all the time for reading e-books from the library, and I have a few Android apps loaded onto it that I use for working on my car and they all work fine. In other words, there’s not really any reason to reflash them, the stock OS is fine.