Cull lines close to another line

Hi guys.

Would be very glad if someone can help.

I have a closed polyline (orange) It could be any shape, for now i am trying with a rectangle.

I need to cull 1 or more lines from this polyline (Red). The ones to be removed are the ones closer to the external polyline (blue).

The reason I want to to this, is because the lines closer to this external polyline, will offset. In other words, I want to select the lines I want to offset and also create a variable offset.

Like the image attached

Thanks