In order to make things easier for me, and because I don't have Windows, I edited the HiyaCFW Helper Python script by jerbear64 and LmN in order to add a graphical user interface to it.

• Allows you to browse for your NAND backup, no need to place it at the same folder.
• Shows the option to choose the output destination, which should be a (preferably empty) FAT formatted SD card or any other folder.
• Downloads the latest HiyaCFW release and decompress it.
• Autodetects the console region from the NAND dump, downloads and decrypts its v512 launcher.
• Creates the patched 00000002.app and bootloader.nds for the custom firmware.
• Uses your platform's twltool (binaries for Linux and MacOS included) to decrypt the NAND.
• Extracts the decrypted NAND to the chosen output destination.
• Installs the HiyaCFW and the patched files on the chosen output destination.
• (Optional) installs the latest release of TWiLightMenu++ on the chosen output destination.

Clicking on the integrated circuit button will give you a NAND mode, where you can remove the No$GBA footer or add it.

• None, everything needed is included in the release archive.

• Python 3.5 or greater with the Tk library (I had to do sudo apt-get install python3-tk -y in my Ubuntu virtual machine, sudo dnf install python3-tkinter in Fedora, sudo pacman -S tk in Arch Linux). You might need to install the Python 3 distutils package also.

• None, everything needed in included in the release archive.

• 7za binaries for Windows, Linux and macOS. It's used to decompress the HiyaCFW latest release as @RocketRobz uploaded it as a 7z archive. Compiled from the kornelski's GitHub repo.
• twltool binaries for Linux and macOS. Compiled from the WinterMute's GitHub repo. For Windows the twltool included with HiyaCFW is used.
• NDS bootloader creator binaries for Linux and macOS (based off devkitPro's ndstool v1.27). Compiled from my GitHub repo. For Windows the ndstool included with HiyaCFW is used.
• fatcat binaries for Windows, Linux and mxacOS. Compiled from the Gregwar's GitHub repo.

See the DS-Homebrew Wiki's Installing hiyaCFW page for instructions on how to use this.

Thanks to:

• jerbear64 and LmN for the original script.
• @RocketRobz for his HiyaCFW fork, its releases and for having the helper script on his repo.
• @Sha8q for the idea.
• WB3000 for his NUS Downloader source code.

Download it from the releases page.