SQL & PL/SQL :: Give New ID To Existing Employee?

want to create a PL/SQL procedure, update_id(id_emp in number), that gives a new id_emp (id_emp=y) to an existing employee (id_emp=x).So before updating the EMP table, we have to :

1- create a new row on EMP(with id_emp=y) that has the same informations of the employee (id_emp=x),
2- update all tables that contains the id_emp column (update <TAB> set id_emp=y where id_emp=x),
3- delete employee (id_emp=x).

The problem is in step 2 : it creates a lot of locks and makes the DB unusable.To deal with this problem, I thought for many solutions, but the problem is how to implement them correctly and efficiently.

Before executing step 2, we have to ensure (through a marker I guess) that all the tables that have the id_emp column, are managed by our session, and any other acces (through SELECT, UPDATE, DELETE, INSERT statment) from another session will be rejected since we have a marker on that table.

When step 2 ends, we release all the tables from the markers.

My simple question : how to achieve this ?