Saving text manipulated data

Hello.

I have a small question/problem.

I have this text file:
<sub>// Test
0
0    0    0    15    15    7    // 0
end

1
1    1    30    25    25    240    240    -1    5    // 1   
end</sub>


I read it into an array in C#, but in my array I read it in as
_{0    0    0    15    15    7    // 0
1    1    30    25    25    240    240    -1    5    // 1}

Since this is a easyer way of manipulating with the data, but now I want to save the data to the text file.
I know the line number of my array, but that does not add up with the orginal file since I stripped som things

So my question is: How do I save the manipulated data so it fits with the orginal data?

My code looks like this:
            _{string[] SaveMonsterLines = File.ReadAllLines(XMLfileLocation);
            SaveMonsterLines[linenumber] = "1    1    30    25    25    240    240    -1    5    // 1";
            File.WriteAllLines(@"D:/output.txt", SaveMonsterLines);}

If you dont understand my question/problem, please speak up :)