Build your own firmware (thanks to @Xandrios)

To build the firmware you need a linux system with a specific toolchain. A linux Debian distro is recommended.

Below an example using Debian 10.

Get dependencies

sudo apt-get update
sudo apt-get install git unzip build-essential libtool bison bison++ bisonc++ libbison-dev autoconf autotools-dev automake libssl-dev zlibc zlib1g-dev libzzip-dev flex libfl-dev yui-compressor closure-compiler optipng jpegoptim libtidy5 node-less sassc sass-spec libhtml-tidy-perl libxml2-utils rsync

Get toolchain

git clone https://github.com/lindenis-org/lindenis-v536-prebuilt
sudo mkdir -p /opt/yi/toolchain-sunxi-musl
sudo cp -r lindenis-v536-prebuilt/gcc/linux-x86/arm/toolchain-sunxi-musl/toolchain /opt/yi/toolchain-sunxi-musl/

Get yi-hack

git clone https://github.com/roleoroleo/yi-hack-Allwinner
cd yi-hack-Allwinner/
git submodule update --init

Compile

sudo ./scripts/compile.sh

Package

sudo ./scripts/pack_fw.all.sh