JPA: how to override column names of @Embedded attributes

Use @AttributeOverride, here is an example

@Embeddable public class Address {
    protected String street;
    protected String city;
    protected String state;
    @Embedded protected Zipcode zipcode;
}

@Embeddable public class Zipcode {
    protected String zip;
    protected String plusFour;
}

@Entity public class Customer {
    @Id protected Integer id;
    protected String name;
    @AttributeOverrides({
        @AttributeOverride(name="state",
                           column=@Column(name="ADDR_STATE")),
        @AttributeOverride(name="zipcode.zip",
                           column=@Column(name="ADDR_ZIP"))
    })
    @Embedded protected Address address;
    ...
}

In your case it would look like this

@Entity
public class Event {
    @Embedded
    @AttributeOverride(name="code", column=@Column(name="manager_code"))
    public Person manager;

    @Embedded
    @AttributeOverride(name="code", column=@Column(name="operator_code"))
    public Person operator;

    //...
}