I tried these procedures, but they failed.
First, there is no /boot/bananapi dir. However, I found /boot/script.bin and modified it as proposed. The new file was also copied to /boot/script.bin.
Second, changing the uEnv.txt does have an effect. If you find the right one ... In my case, it was /boot/bananapi/bpi-m2p/linux/uEnv.txt.