Master of Orion Savegame Editor

Save slots are defined in CONFIG.MOO, so if you never saved in slot 2 in the game, placing SAVE2.GAM in your game folder won't make it appear in the game. Simply save a game in slot 2 first, then overwrite SAVE2.GAM and you can play your modified save.

The player (you) is always the first in an array of six (e.g. players, ships-and-research, ...) at array index 0.

If you want to unlock research in ships-and-research.unlocked-research-*, don't forget to set players[n].amount-of-*-researched to the correct amount, otherwise, your added research won't be counted.

If you want to upgrade your ship, you'll notice you can't reduce the cost (it's recalculated every turn based on the properties of the ship). To cheat in some ships, you can go to your planet and set ship-building-progress to e.g. 32000 (it's a signed 16-bit number).
Alternatively, go to player[n].planet-orbiting-ships, find your planet and change the amount of ships of each type that are orbiting the planet.