I don’t know all the functionality differences, but default assignments is one. And I know the developer recommends not repurposing control accounts. Renaming is okay.
I’m still not sure it should be possible to rename built-in control accounts if there are custom control accounts.
I know it looks like a bookkeeping error but Manager will automatically correct this even if the wrong control account is selected. The money will still flow to the correct customer / invoice.
The question is not whether you can do it. You can. The question is whether you should do it, because of the default functionalities. The developer recommends that you not do it. When it is so easy to create a third custom control account, why would you ignore his advice?
To view receivables in different area, if I create different custom control account for customers and assign customers to those control account, it’s OK, right?
To view profit in different area, I have to create divisions, assign divisions to customers,and select divisions to every line item in sales invoice or receipt, right?
For your second question, if you have assigned a customer to a division, you should not need to make assignments on individual line items for transactions with that customer.