Managing order adjustments – help!

I’ve spoken to Woo support and I’m still finding it difficult to understand something. I am moving to Woo from a different platform that functions quite differently.

If you have received an order from a customer, and then they phone or email to say they want to add an item to the order, or they chose the wrong variation, or they want to change to a faster delivery, etc, something that requires adding cost to that order… how do you process this?

From what I understand you have to change the order status back to Processing, and then add the item or fee, and then email this to the customer. But the recalculation gives a new total for the whole order, that the customer already paid for, and not just the additional amount that needs to be paid.

If the customer wants to just add another item, you could create another order, but the site I am making has a minimum order amount so this wouldn’t work. And it would be better to also give them one order and invoice. If they wanted to change to a faster shipping and pay the extra, how do you email them to pay the extra?

I am finding it difficult to understand how to manage and deal with these scenarios. Could anyone explain how you do it?

Many thanks