Downgrading is the act of reversing a software update.
There are a variety of reasons to downgrade StarCraft. Many mods only work with certain versions of the game, and users with later versions have to downgrade to use them. Maps that use EUDs only work on specific versions of the game, as patches change the locations of the game's data and invalidate the maps' triggers.
Downgrading StarCraft manually simply requires that you "hide" your previous installation of the game, reinstall it from the CD, find the desired patch on Blizzard's website, and then apply it. This results in you having two separate copies of StarCraft, with different versions.
- Open the Start Menu. Select Run..., type regedit, and click OK.
- A new window -- the Registry Editor -- should appear. Its left panel should contain a tree view. Open HKEY_LOCAL_MACHINE.
- Open SOFTWARE.
- Scroll to find "Blizzard Entertainment".
- Open that folder, and open the StarCraft folder inside.
- In the right panel, right-click on "InstallPath", and select Modify.
- Change the value to a directory that doesn't exist, or simply delete the path string.
- Insert your StarCraft CD, and re-install the game.
- Download the desired patch from Blizzard's FTP site. Apply it.
- Run StarCraft.
Note: Installing StarCraft a second time modifies the registry keys (specifically, the "InstallPath" key mentioned above) to refer to the new, downgraded StarCraft. As a result, programs that depend on this key (including MemGraft patches) will affect the newly-installed StarCraft. When you use the AutoRun, it will run the downgraded StarCraft. To play on Battle.net, make a shortcut to your current (first) version of StarCraft and run that instead.
SCDowngrader is a utility created by FaRTy[MM] aka O)FaRTy1billion. It automates much of the downgrading process. The utility is currently in its third version, which doesn't require the user to have copies of every patch. (Only the desired patches need to be loaded into the downgrader, and they may be obtained at the utility's website.) Those using the previous version (which came with every patch built-in) can update using a specialized installer, without having to download all of the program's files.