in simple words, TM 3 is open loop MIMO and TM4 is closed loop MIMO.
open loop MIMO:
in this case ENB will use mimo transmission without considering PMI feedback from UE. PMI is precoding matrix indicator which is used in precoding.
closed Loop MIMO:
In this case ENB will consider PMI feedback for UE and transmit data according to it.
TM modes are decided in one shot at ENB configuration, say if enb supports TM4 then for all the UE it can use max TM4(like TM1 to TM4) mode if UE supports.