How Can I Duplicate A High Poly Scene, Without Driving The Geometry Through The Roof?

I need to duplicate, and change slightly this file, without driving my Geometry SKY HIGH! The current Geometry is about 300,000 verts/faces, and I’d like to keep it low so I don’t totally DESTROY my computer! I’m in the loooooong miserable process of downloading Linux, which shouldn’t crash Blender like windows… :smiley: Until then, I need an effective way to do this… Any help would be greatly appreciated!