At the BattleScape screen, press [Ctrl] C to complete the current level and advance to the next one.
Select an item to be manufactured, but assign no engineers and leave the number to produce at zero and click OK to get back to the base management screen.
Then go back into manufacturing and assign as many engineers as you desire but only manufacture one item.
The item will cost you nothing to make, and you can sell it for money, or use it later.
Before finishing a mission, be sure to unload all weapon clips including those found on aliens. If you don't, any loaded clips will be lost and you'll have to make more.
Inherit Previous Knowledge
NOTE: This involves copying files from saved games, so make a back up of your entire game before hand.
In the game directory, you should see a saved games folder with each of the ten save game slots with Game0, Game1, Game2, etc. On your most advanced game i.e., with the most research unlocked copy the following files:
to a new saved game just start a new game and save five seconds into it on another slot and you will have all the necessary knowledge on the aliens to use their weapons and manufacture their craft depending on how much you researched in your old game.
You can also keep powering up your soldiers by copying the soldier.dat file into your new game - just be sure the number of new soldiers is equal to the number of old soldiers you are transferring from your old game, or the game will crash. You can hold over the stats of your soldiers from your old game into the new one so you can keep having them earning experience.
The soldier.dat file also has the armor worn by the soldier, so if you need extra armor do the following: strip the armor from your "current" soldiers, save the game, copy the soldier.dat file again, and sell the armor you stripped.
Last note: keep only the soldiers with a high psionic strength around 80 or more is good. Psionic Strength is the only soldier attribute that cannot be improved everything else can be, so it's best to keep only soldiers with high Psionic Strength to resist mind attacks from the more deadly aliens.
NOTE: This involves copying files from one save game to another; this trick has a very high chance of corrupting your game.
The craft.dat file has not merely your current craft in the hangar, but lists the aircraft in the air as well including UFOs. The "cleanest" craft.dat file the least possibility of it corrupting a game, is to have two Fighters and one Skyranger in your hangars, with no UFOs in the air. Save the game and take that craft.dat file.
The craft.dat file not only records the aircraft in the air and in storage, but also what is loaded into the aircraft. Load a Skyranger with 80 items and you can "transfer" the items by copying that craft.dat file into the save game that you want.
80 Mindprobes will net you about 2.4 million dollars through their sale. This is also a good way to get extra clips or blaster/stun bombs if you are running short.
Keppin mind that UFOs always show up in the game, so try not to do this trick often, or you will corrupt your game when a UFO or one of your own aircraft is in the air when you do this file swap.