title: How in C# to reformat string, representing a decimal, to have space group separator?
body: <p>I have found on SO some posts, regarding formatting strings, representing numbers, to have digit group separators, during converting decimals (or other number data types) to string:</p>
  
  <p><a href="https://stackoverflow.com/questions/2100472/how-to-format-1700-to-1700-and-1000000-to-1000000-in-c">how to format 1700 to 1&#39;700 and 1000000 to 1&#39;000&#39;000 in c#?</a></p>
  
  <p><a href="https://stackoverflow.com/questions/1142994/c-formating-price-value-string">C#: Formatting Price value string</a></p>
  
  <p>What if I have these numbers already in string format (have read from a .txt file by StreamReader), but want to have group separators nevertheless (and in string format)? </p>
  
  <p>Is parsing it to decimal and then back to string with needed formatting the most reasonable way in this case?</p>