A method to create halos on multiple lines without any visible overlap of the halos?

Question

I'm struggling to find an easier way to create a uniform halos on overlapping line. It needs to be reversible. Meaning I can change it whenever I can.
Header 1
Header 2
Currently I am using a method that is time consuming, requires a lot of planning and it non reversible. I always select all the lines (hopefully I got them all), Use "expand", and then "shape mode" (Unite). Use an "offset" and the paint it black.
This works really good, however, the major drawback once I do the expand. I can't modify anything on the drawing, let say if I want to change it to a to a smaller/larger page or move a line... then I am screwed.
The second method I do is the fastest but also the ugliest. I use the appearance tab to add another larger "stroke" with a white color. Easy and fast to apply and change. But the end result is no good. The halos are not outside all the lines....Is there another method to do this and it is still reversible, or at least to a stage that is much later than the above?
//Vincent

Answer 1

if you group the black lines - without first applying the white stroke - you can apply the stroke at the group level in the appearance panel, then move it so it is below the group contents. then it will appear below all of the black lines, not individually.