Replacing HR Module Doctype by another Doctype from our custom app

We are planning to create a new Employee Doctype under our custom app, instead of simply customizing the Employee Doctype available in the HR Module since there will be too many changes that we think it would be better for us to start from scratch.

Our problem is wheter it is possible to change the form used under HR Module using our own Employee Doctype? And in addition, is it possible to load a different Employee Doctype depending on the role?

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