test.cs

 private static void RenameMergeBlocks(SubTextPartCollection subTextParts,
                                       string oldColumnName,
                                       string newColumnName)
 {
     // iterate through all SubTextParts
     foreach (SubTextPart subTextPart in subTextParts)
     {
         // check if the SubTextPart is a merge block
         if (subTextPart.Name == "txmb_" + oldColumnName)
         {
             // rename the SubTextPart
             subTextPart.Name = "txmb_" + newColumnName;
         }
     }
 }