So the mcu will receive command through the Rx line and then it will start sending through the Tx as an answer to the request.
If there is no case when the Rx will receive data while the Tx is transmitting then the transmit signal will go to the through plug fine (assuming it can drive the 1k8 resistor) but the problem is when you are in receive mode, in this case if the TX pin is either low or high you will have problems.
One solution I see is to use the TXENn: Transmitter Enable bit flag to disable the Tx operation and set the pin as an input with no internal pullup, this will actually make the Tx pin a high resistance input so it will not have a problem with the Rx signals, you have to check if this is actually the behavior of the pin because I haven't done anything similar.
Also to disable the Tx pin the transmit buffer has to be empty.
Alex