10 December 2019
Just to make something clear you will still need to designate a contact and target in each pair, if you are using auto generated contacts ANSYS will select the pair automatically. For symmetric behavior though it does not matter which surface is the contact and which is the target, so assuming this is what you mean by specify you are correct.
Be aware though the results given by the symmetric behavior are not as straightforward as asymmetric. For example lets say you are looking at contact pressure, symmetric behavior gives you results on both contact surfaces but the true contact pressure is an average of both of the surfaces. While asymmetric results which are only on one face are the true contact pressure.
If you have any other questions let me know.