Convert polygon lyr to line or an alternative

Hello,

is it possible to convert a layer file, made of a polygon shape, to a line format so that I can use it for a line shape?

Here is what I want to do:

I have a polygon layer with thousands of features and an ID field. And a line layer, like a network, with a corresponding ID field. Many polygon features belongs to one line feature. They do not necessarily intersect.
To visibly check the correctness of the ID fields, I choose a "Categories - Unique values - Add All Values" symbology with a Color Ramp. Now I want to have the lines the identic colors as the polygons. I thought about creating a layer file, in that all IDs have a specific color, and convert it somehow to a line layer file. The fill colour of the polygons should be the color of the lines.

Is there another way to accomplish this?

Thanks for your help.