Change outline color ?

You have used "Outline" from the pathfinder panel?

The result is a group. If you ungroup it and then take a look at it in the Layers panel, then you can see what you get and can select the objects and change them. The objects will also have a very thin stroke and you have to change that or it will be invisible when printing.

If you want to change just some strokes, that will get difficult  but can be solved when you set up the base objects accordingly. So if you describe what you want to get, then possibly it can be achieved in an efficient way.