The mod can be found here in its current state.
Put it in your Documents folder, usually found here (replace UserName with your User Name).
C:\Users\UserName\Documents\My Games\Cosmoteer\Mods\
Then activate it in the game and restart.
Then choose a new game and select the difficulty level of 'Legendary'.
Depending on the 'size' of the galaxy you choose, will depend on how hard the game is. Huge galaxies are easy, because you have more low level systems to build up your cash supplies. Smaller galaxies would be harder, because you have fewer systems.