How do you replace imported 'proxy' objects with Library objects?

1. Here's how

The Place item on nodes function lets you place objects of your choice at the same positions as imported proxy objects from your 3D/CAD software.

Each proxy object should be a separate object, for example simple duplicated boxes.
Make sure that a single material is assigned to all faces of the proxy objects.
The function works with Revit, SketchUp, ArchiCAD, AutoCAD, AllPlan, 3ds Max and Rhino.

See the steps and export requirements for each of these applications in section 2-8 below.

1.1: Lumion 9.0 and newer

After importing a model with proxy objects and placing it in your Scene, use the Place item on nodes function to place an object of your choice on each of the imported proxy objects.

The function is available in the Object Options panel for Imported Models.

If a Windows Open File window pops up when you click on the Place item on nodes button, select the Imported Model file with the proxy objects, and click on the Open button.
Please note that when you use the Place item on node function in Lumion after importing a model file, it will place additional objects at the Object Icon of the model. Simply delete those objects.

1.2: Lumion 8.5 and older

After importing a model with proxy objects and placing it in your Scene, use the Place item on nodes function to place a tree/plant or light of your choice on each of the imported proxy objects.

The Place item on nodes function is available in the Extra menu in the Context Menu for Imported Models.

If a Windows Open File window pops up when you click on the Place item on nodes option, select the Imported Model file with the proxy objects, and click on the Open button.
Please note that when you use the Place item on node function in Lumion after importing a model file, it will place additional objects at the Object Icon of the model. Simply delete those objects.

2. Guidelines for Revit

2.1: Install the Lumion LiveSync for Revit plug-in if you are using Revit 2015 or newer:

Knowledge Base: Download Lumion LiveSync for Revit

2.2: In a 3D View, place some simple objects, e.g. columns or boxes, to represent the proxy objects. Make sure that a single material is assigned to the objects.

2.3: Tick the Export nodes button in the Export as Collada file settings before exporting a .DAE file to Lumion:

2.4: Follow step 1.1 or 1.2 above.

3. Guidelines for SketchUp

3.1: Create a box for use as a proxy object. Make sure that you have only assigned a single material to all faces of the object.

3.2: Right-click on the box and select Make component.

3.3: Duplicate the box as many times as you want. Do not group the duplicates.

3.4: Lumion 9.0 and newer versions:

Save the model as an .SKP file.

3.5: Lumion 8.5 and older versions:

Select File -> Export -> 3D Model, choose Collada file (*.DAE), click on Options and make sure that Preserve Component Hierarchies is ticked before exporting the .DAE file.

3.6: Follow step 1.1 or 1.2 above.