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From time to time, you might want or even need to make changes to system files that are more or less critical. This can be risky business, and as a result, it is always smart to make the changes in a non-operative version of the file, then back up the file, and only then implement the new version.
A practical example; You want to change the OEM-info of your computer. The way you do this is first to locate and make a copy of the OEMINFO.ini-file, then make the changes in the copy. Once you’re done, you rename the OEMINFO.ini-file to OEMINFO.ini_old, and only then do you actually implement the new file, copying it back in.
The reason for this is twofold; firstly you’ll not be screwing up anything while editing, and should something go wrong, it’ll be that much simpler to roll back; simply rename the original file and you’re back up and running.