您应该能够分配该元素：

You should be able to just assign that element:

arrLine[yourLineNumber] = "Foo";

我实际上如何将更改提交到文本文件？

how would i actually commit the change to the text file?

完成此操作后，可以使用 File.WriteAllLines（pathToFile，arrLine）; 将数据写回到原始文件。

Once you've done this, you can use File.WriteAllLines(pathToFile, arrLine); to write the data back to the original file.