Hi,
Yes, you can still use these objects in a population. What you're saving in the clip file is basically an object node with your tweaked settings, plus the material shader nodes and such. You can connect object nodes to populators, you don't need to do at the time the populator is created. When you insert the clip file the nodes from it are added to the network and can then be connected as per usual. Here's one way to do it (assuming you're using a TGO object in the clip file):
1) Choose to create a TGO population from the Add Object button in the Objects node list.
2) When the file dialog opens for you to choose a TGO file for the population just click the Cancel button. This will create the populator node and make the default connections (connecting to the planet for example). It will add a TGO reader node which hasn't got a file but you can delete that.
3) Insert your clip file
4) Go to the new populator node's parameter view.
5) Click the Assign Node button (green plus icon) at the right of the Object make parameter.
6) From the menu that pops up go to the "Assign Object" submenu and choose the TGO reader node you've inserted with the clip file.
7) Go to the TGO reader node and check that the Population mode parameter is set to "Member of a population".
Now you should be able to populate as normal. It's quicker to do than explain :-).
Regards,
Jo