suppose I have created a string in C# and I want to change the last character to a blank.

private static string sOldMassiveOutput;

public static string oldmassiveoutput
{
get { return sOldMassiveOutput.Trim(); }
set { sOldMassiveOutput = value; }
}
oldmassiveoutput[oldmassiveoutput.Length - 1] = ' ';

This will not work.
How do I make it work?