Summary:

Set New Person as Default Person for Company

Description:

1. Go to Administration > Customisation > Person 

2. Choose Screens and open ‘Person Entry Screen’

Description

3. Add the below code in Custom Content

<script>

    crm.ready(function()

    {

        var actionId = crm.getArg("Act", crm.url());       

        if(actionId == 221)

        {      

            $('#DefaultPerson').attr("checked", "checked");

        }

        var companyId = document.getElementById('pers_companyidTEXT').value;

        if(companyId != '' && actionId == 141)

        {                 

            $('#DefaultPerson').attr("checked", "checked");

        }

    });

</script>

Description

It will set your 'New Person' as Default Person for the company and remove the previous one.

Note: 

Please take backup of the database before making any changes.