Acknowledged mode of operation is supported by SDCCH, SACCH and FACCH.
I think that all MM and CM Layer3 messages are transfered by Layer2 in acknowledged mode.
Remote data link entity acknowledges a received frame by means of I-frames or S(supervisory)-frames.
Acknowledgement (N(R) – last properly recieved frame) is contained in control field of I- or S- frame.
If you will increase T200 there will happen nothing. What is your objective?