For absolutely no changes to your object as it appears/positioned in the scene: export with all options unchecked (unless you want to consider groups, in that case 'include existing groups'). With all options unchecked no transformations will be applied during the process, what you see is what you get. Parent the prop, save to library, select yes: as smart prop.

Edit_Leave all options unchecked during import. You don't need any of that.

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