How to merge specific customer accounts from one customer to another customer

We have requirement to merge the customer specific accounts from one customer to another customer.

Business Scenario- Customer acquiring part of customer accounts from another customer, need to have partial merge. Creating new accounts under the acquiring customer will not work because there will be lot of manual work involved, as we have open invoices, Credit Memos etc.

Below is example -

We have 2 customers A and B. A customer having 10 customer accounts and B customer having 15 customer accounts. We want to merge 5 customer accounts out of 10 from A to B customer. Those 5 customer accounts should be assigned to the B customer legal entity. After Merge we want to have A customer having 5 customer accounts and B customer having 20 customer accounts.