Beginners question in multiple assignments to output

What you seem to be asking for is analog logic, summing the levels on two wires to produce an output signal that can have three discrete levels.

IE: (0,1) + (0,1) = (0,1,2)

This is not possible in digital logic FPGAs.

At best you could two outputs and resistors to simulate a simple digital to analog converter, much like some development boards support an analog VGA signal using an array of resistor values R-2R-4R-8R etc to make a simple D to A.

Can't be done internal to a device however. Not with any current Altera FPGA parts AFAIK.