I don't know what to alter in a savegame file (and I don't know where the savegame files are located either).
However if you want to help yourself earn more credits, you can earn 100K in roughly one hour by resetting the commodity exchange inventory.
First you buy all the wood, let's say. Then you save, and then load that exact save. You will find a lot more wood for sale. Get a full 125 unit load.
Fly to the Star base. Then sell the wood and buy all the Tungsten, Gems, and then Iron (For filler) you can. Save and reload the save.
I do this a maximum of three times for the Tungsten (best profits) and Gems (next best). After 3, I simply fill up on Iron (lowest profits) and then fly back to the planet.
Rise and repeat. It's a bit boring but you will see your credits rake up very swiftly. With the apx. 100k / hr, 7hrs of grinding will net you 700K, enough for a nearly tripped out Centurion or the larger trader ship (can't remember it's name, it's too early in the morning).