I placed many objects via Overlay Editor,however,I want to add more variations,but to the same "object calls",is there any way that I can force XP10 load random OBJ's to the same spot? 

Yep, create an object library for your scenery package and map multiple objects to the same virtual path using EXPORT_EXTEND or EXPORT_RATIO library directives then place the object in your scenery from the library. The sim will pick amongst the multiple definitions when it renders the scenery.

 

More here: http://scenery.x-plane.com/tutorials.php?doc=library.php

Will look into it,thanks!