There is a much better solution. 
Below the position "Retained Earnings" you create THREE subpositions. You do no have to show them.
1. Position: Retained Earnings manual accounts --> assign the retained earnings accounts. On those accounts you should have only postings from first data-migration; Usually I am working with account-tags.
Presign is "-"
2. Position: Retained Earnings Total --> here you assign all p&l accounts and say "from the beginning"
Presign is "-"
3. Position: Retained Earning Current Year -->  here you assign all p&l accounts and say "from the beginning of current year"
Presign is "+"

Finally you sum them up all together!
No year end booking is needed! Never ever 

Do you mean Current Year Earnings?

You create a Journal Entry to move Current Year Earnings to Retained Earnings.

See https://www.odoo.com/documentation/user/10.0/accounting/others/adviser/fiscalyear.html