It sounds like you aren't aware of the ability to insert orders. 🙂 Click on an order to select it (in white), and then any orders added will appear above this.

I'm not talking about positioning of the order, but its "specification", like "transfer and leave empty" or "Unload and take cargo with refit to wood".

I understand this problem, although it doesn't seem particularly big to me. One question that comes to mind... @RoqueDeicide: Are you using shared orders?
Even so, I don't think it would be a bad thing to add a replace destination function while keeping the specs of the previous target. This function could be listed under "Go To" when the player mark an order in advance.

"Shared orders" feature is irrelevant here, as I'm suggesting ways to expedite editing of the orders list, "shared orders" simply propagate the edits.

Although I understand what you are asking, our issue tracker sadly enough is not the right place for such feature request. Best is to create a topic on https://tt-forums.net to collect if others agree and what a good approach would be. From there someone might pick it up to program this in the game :)

Personally, I like what you suggest; just no clue what the best UX approach is for it .. something to think about :)