Mc._name property is readonly?

In fact: I duplicate an mc in rows and columns, and want to change their location (_x,_y),
my problem is: I want to change also their name

mc1_mc move to mc2_mc._x and viceversa
firstName = mc1_mc._name;
secondName = mc2_mc._name;
// renameing
mc1_mc._name = secondName;
mc2_mc._name = firstName;
// but this part is not working

In flash 6 exist the setName function, or is a readonly property?