Please use FULL words to write your message!!! If you are in a hurry to write this up properly why should anyone take their time to prepare a proper answer for you.
?1) Is this a method that is called after the order is filled ? -> yes it is but to make sure we also do an extra check up
if (execution.Order.OrderState != OrderState.Filled) return;
?2) ? how and where are the OnExecutionUpdate overloads affecting the process ? - it is not clear what you are trying to ask here
?3) Line 543 makes sure that the order filled does NOT have a name EnterLongName or EnterShortName,