I love Google Earth but they stopped most updates and are pushing users toward Google Maps.
One nice feature with Google Maps, is once it sets a route, you can click and drag to force an intermediate stop. So if you have way-point you want to hit or a place you want to avoid, just drag the route to or away.
Is there a reason, you are trying to export it to Google Earth? They have an automated option to send it to your phone version of Google Maps, so you can use it in the car. If you really need to do it, there are some after markety tools you can download to a KLM file but I haven't messed with them as I haven't needed them.
