Hello john,
You would need development for something as specific as that.
Regarding credit that message will appear when trying to add a new order depending on the credit limit on the customer card.
Credit hold again would be set on the customer card
You could set up a flow/approval for the credit limit check
(I set the credit limit to new customers as 0.01 as if left at 0 that is unlimited credit at 1p it flags the credit limit warning, meaning the credit limit has not been set by account yet
Not sure on the last one customer needs to make a change they would inform you the change you can reopen the order then amend and then release again