If the TA keeps the middle name blank, will the middle name from DL populate through on the ticket or do I need to call DL after TA provides PNR?
If I have to call DL, is it difficult to have changed?
Your TA should be using your full legal name on all tickets, so that the ticket matches your travel documents. Your need to update your record with your regular TA (or fire that TA if they insist on doing this wrong). It's hard/impossible/expensive to make a name change after a ticket has been issued.