What is the best way to create a desktop environment for Linux Mint and get an ISO

[hydroperfox]

I want to fully change the Linux Mint Cinnamon interface. Non-exhaustive list of intents:

• Start Menu (it is not a popup that shows over the taskbar, but rather an ordinary menu)
• The taskbar drag-n-drop of fixed icons
• Touchscreen gestures
  • In taskbar
  • In minimization, maximization, and division of windows
  • In the bottom-right corner of the screen (to show up time, weather, and a navigation bar containing big icons simultaneously)
• Skins and icons
• Application skins
• Easing transitions
• 3D transformations in 2D components through CSS (already possible in Cinnamon themes, but there are additional complexities there)

Is it legal to fork the Cinnamon repository and build the desktop environment after cloning all dependent upstream repositories from the Linux Mint organization?

From the reference Part II. Building Cinnamon: how will I get a disc image (ISO file) that I can mount in a flash drive after building the repository in a Debian system?