** Since I have 2 black wires, does it matter which black goes into "load" and which black goes into "line?" **
Yes, the 'hot' one should go to the 'line' side of the switch so its power is terminated by the switch when off and not the neutral, leaving the hot line 'live' all the way to the fixture. That could be very dangerous!
Since someone has changed the wire colors, each will first have to be tested to see which is actually the 'hot' line of the electrical circuit.