repalce parts of textfile

dear all.

i have a textfile which is built like this:

Quelle 120 20 *MF.Quelle

Senke 160 40 *MF.Senke

...

Now i want to move the created objects in unity (information comes from textfile) and rewrite the textfile so it looks like this

Quelle 160 40 *MF.Quelle

Senke 260 60 *MF.Senke

...

so i just need to replace parts of my textfile while the rest keeps equal.

i managed to write a textfile with following code but that is just for writing a new textfile and not rewriting the old one. i am only able to find a way to delet specific lines and write specific lines but not just parts of a line.

     public void Button_export()
         {
             writer = new StreamWriter(path, false);
 
             A = GameObject.Find("Quelle");
             pos = A.transform.position;
 
             var ANAME = A.name;
             var AX  = pos[0];
             var AZ  = pos[2];
             
             writer.WriteLine(ANAME + '    ' + AX + '    ' + AZ);      
 
 
             B = GameObject.Find("Senke");
             pos = B.transform.position;
             var BNAME = B.name;
             var BX = pos[0];
             var BZ = pos[2];
 
             writer.WriteLine( BNAME + '    ' + BX + '    ' + BZ);
             writer.Close();

some one knows an answer? thanks in advance