Matty R said:
Couldn't I just keep a note of what I've changed? Please don't get all technical on me. I'm young and impressionable.
I like to keep things structured and organized, but that's just me. I don't like the thought of reinstalling civ4 just because I don't know exactly what I've changed anymore. Keeping a note on everything you change is probably a lot more work than creating a minimod out of it. I've never created a mod for civ4 before, but I think it is very easy (I have created a mod for civ3). There's probably a tutorial for this in the creation and customization section of this forum.
If you want to create a mod out of it:
A) Go to the mods directory and create a directory 'My great mod' (or something more humble if you like).
B) The file CIV4BuildInfos.xml is in ...\Civilization 4\Assets\XML\Units, so you have to create a similar directory structure in your mod: Civilization4\Mods\My great mod\Assets\XML\Units. Place a copy of the file CIV4BuildInfos.xml in that directory and mod it to your heart's desire. Now your mod is finished. (The game will look for modded files in the My great mod directory and when it doesn't find a certain file it will look in the main Civilization 4 directory. So it isn't needed to have a copy of every gamefile in the 'My great mod' directory.)
C) When starting the game you can choose your mod from the Main Menu or you can mod the civilization4.ini file so that the game automatically starts loading your mod.
At present the civilization4.ini file has a line:
; Specify a Mod folder (Mods\Mesopotamia), '0' for none
Mod = 0
To change this so that it automatically loads your mod you probably have to change this to
; Specify a Mod folder (Mods\Mesopotamia), '0' for none
Mod = Mods\My great mod
Now it is very easy to disable your mod. You just have to change the civilization4.ini file back to normal (replace Mods\My great mod by 0 again).
By the way, why do you want to change the building times of improvements so drastically?