"TK" Code on Sabre
 

My TA recently emailed me my flight itinerary from his sabre screen. On one of the segments, it showed the "TK" code on one of the flight. I know that this means my "confirmed" flight had undergone a schedule change (which is not a big time differential on my flight BTW). Hearing from people who work at agencies using sabre, they said that the "TK" code can be changed into "HK" which is the code for confirmed bookings that doesn't undergoe schedule changes. My question is it necessary for my TA to convert the "TK" into "HK" on his sabre system? Will anything happen to my booking if he does not convert the "TK" back into "HK"?

Yes, your agent should advise you of the schedule change, and then change the status to HK to acknowledge it.