Can we use <replace> in the Entity?

I want to change the relation of contactPartner (in HR) from one-to-one to many-to-one
so, is there any better option to change the default relationship ?

<replace>
      <!-- Elements to replace the target element with -->
</replace>

You cannot,

You need to create a domain file in your custom domain, with the same name that the existant HR domain.
Add a many-to-one with a similar name, and replace in your form the field which display the one-to-one to replace by your field.
Never use the relation to the one to one.

I have deleted the one-to-one field that exist in the Axelor HR Module.
And add a new field in extended domain/entity, with the same name and it work fine for me.