Online Maps does not check if this value changes in the inspector at runtime due to performance reasons.
How to change the location marker texture at runtime:

(OnlineMapsLocationService.marker as OnlineMapsMarker).texture = newTexture;
OnlineMaps.instance.Redraw();

I am using: OnlineMapsLocationServiceBase.marker2DTexture to change the marker texture. This works during the first time (for exemple during start), but it seems to work only once, car if I change the texture later it does not changes the exture.