You can use one of the following flags as the last argument to SaveStringToFile() to control how the file should be written:
FILEWRITE_None
FILEWRITE_NoFail
FILEWRITE_NoReplaceExisting
FILEWRITE_EvenIfReadOnly
FILEWRITE_Append
FILEWRITE_AllowRead
By default SaveStringToFile() will create a new file if it does not exist, and if it does already exist then it will be overwritten.