hi,
thanks @mp5gosu for the answer.
About inserting material before making some changes, there's no real right way of doing it. It just that if something go wrong about the change you are doing, you have to remove the material from the document, while if you don't insert it, you don't have to.
As @mp5gosu said it's better to insert the object in the document before linking them. Even if should work if you insert the material after.
Cheers,
Manuel