Enroute

Yes you do need to "Actually" attach them to the boot L0 because it will give an error telling you that you have multiple extra 1 L0's and extra 4 L0's.

Yes, You could simply drag and drop the L0's (from whatever light your are trying to attach to the boot) to the boot file inside your vehicle hierarchy and an then attach them there so they can open with the trunk in game.