test.cs

// find the SubTextPart
SubTextPart mergeBlock = textControl1.SubTextParts.GetItem("txmb_location");

// create a new MergeBlockInfo object from SubTextPart
TXTextControl.DocumentServer.DataSources.MergeBlockInfo mbInfo =
  new TXTextControl.DocumentServer.DataSources.MergeBlockInfo(mergeBlock);

// add a condition:
// render block, if "id" from parent is greater than 1
mbInfo.BlockMergingCondition.Add(
  new TXTextControl.DocumentServer.DataShaping.FilterInstruction(
    "id",
    TXTextControl.DocumentServer.DataShaping.RelationalOperator.GreaterThan,
    1));

// apply conditions
mbInfo.Apply();