Depending on your workflow and how you set up your initial import. In bigger companies this is the first thing to be customized out of such issues, but UE would need to know where to get the information from.
So the easiest solutions would be, to import as many individual parts as possible and only reload the ones which got changed, writing scripts to handle your changes and write them back to the new import or store information separated somewhere else.
You could get your spline and get it’s length to determine how much space it’s still left (just some of the functions you might want to use):
I’m not completely sure what you’re doing. If your McLaren is already a BP and a Actor of some sort in your scene, you would probably attach your ‘icons’ (probably planes?) in the component tab of the already existing McLaren BP to have them always aligned with your car, even if it’s moving. If they should disappear while driving you could just hide them. 
Don’t know if this helps, if not I would need more information what you’re doing.