GregTech configuration files go to Ultimate\minecraft\config\gregtech, with the important files being "Recipes.cfg" and "Gregtech.cfg". If you can't find your minecraft install directory, it should be listed on the Options tab next to Install Folder...
Important changes in
Gregtech.cfg :
Under "features" :
b:ForestryBronzeNerf - when true, returns two (or one, in more recent versions) Bronze per three copper and one tin.
Under "machines" :
b:Constant_Need_Of_Energy - when true, gregtech machines will lose progress if the device loses power, even for a split second.
b:explosions_on_nonwrenching - when true, gregtech machines will explode if you pick up with a drill or fists.
b:fire_causes_explosions, b:machines_flammable, b:lightning_causes_explosions, b:rain_causes_explosions - when true, makes gregtech machinery explode if on fire, struck by lightning, wet by rain, or looked at funny.
b:wirefire_on_explosion - when true, exploding machines will send pulses of increasingly high voltage back up their connected wires.
In
recipes.cfg, the most relevant bit is under "usefulrecipes":
B:BeryliumReflector - when true, requires a Berylium Cell instead of a Thick Copper Plate for Thick Neutron Reflectors, used for nuclear stuff.
B:Compress2Storageblock - when true, allows a compressor to turn Ingots into Blocks. Setting to false will allow you to do it by hand at a crafting table, although you can also tweak individual types of ingots in other parts of the recipes.cfg
B
ifficultIridiumPlate - when true, requires an implosion compressor to make Iridium Plates, as well as complicating their creation in other ways.
B:ElectricSteelTools - when true, requires steel instead of refined iron to make the mining drill and similar tools.
B:ExpensiveBCQuarryRecipe - when true, requires a Diamond Drill instead of a Diamond pickaxe to make a BuildCraft quarry.
B:ExpensiveLaser - when true, requires titanium and a coolant cell to make a mining laser.
B:ExpensiveMaceratorRecipe - when true, requires diamonds instead of flint for the Macerator.
B:ExpensiveNanoSaber - when true, requires platinum, iridium, and higher tier components for the Nano Saber.
B:ExpensiveNukeRecipe - when true, makes the hidden Nuke recipe more expensive.
B:ExpensiveSolarRecipe - when true, vastly increases the cost for Solar Panels, as well as Advanced Solar Panels (if installed).
B:ExpensiveWatermillRecipe - when true, requires aluminum ingots to make a Watermill, instead of sticks and wood.
B:ExpensiveWindRecipe - when true, requires carbon or magelium plates to make a Wind Mill, instead of iron ingots.
B:MMIngotOnlyRollingMachine - when true and Railcraft is installed, requires a Rolling Machine to make mixed metal ingots.
B:Storageblock2Macerator - when true, allows a macerator to turn Blocks into several dusts. Setting to false will allow you to do it by hand at a crafting table, although you can also tweak individual types of blocks in other parts of the recipes.cfg
I:TincellsPer4Tin - sets the number of cell per tin recipe. Default is 4 or 8, depending on version, while IC2 usually allows 16.
B:TitaniumDiamondDrill - when true, requires titanium in addition to diamonds when upgrading to a diamond drill.
B:ToolAndArmorMaceration - when true, allows the macerator to turn armor back into dust.
B:WatermillReverseCrafting -
Note that, if you're playing on a multiplayer server, that these changes must be made on both client and server, or you will encounter errors.
Apologies I can't speak Italian.