Am I right that you enter an item receipt with an item with track landed costs marked, then create a vendor bill with for example you're freight charge item and after that you go back to your item receipt and link the newly created vendor bill to the item receipt?

Yes, that is how you would do it, if you are linking a specific vendor bill that has come in after the time at which you receive the goods.

You can also put in a free hand amount.

Alright, like I thought. Thanks!

exactly

you can use Inbound shipment management and you can update those landed cost until the accounting period is open I think, not sure if you looked at that option.