SharePoint 2013 – URL mappings for Host Named Site Collections
The only way to add a URL mapping to a Host Named Site Collection is by using PowerShell and the Set-SPSiteURL cmdlet. Below is an example of how to add a URL to an existing site collection:
$Site = Get-SPSite ‘https://intranet.webbworld.local’
Set-SPSiteURL -Identity $Site -URL ‘https://portal.webbworld.local’ -Zone Intranet