To change or update URLS after resotring a content DB of hostnamed site collections, use
stsadm -o renamesite -oldurl http://abc.com -newurl http://abc-uat.com
You only need to rename the root hostnamed site collection. It will reflect on the other HNSC starting with the same URL.
If you try using Set-SPSiteURL on an HNSC with same starting url, you will get the error : Could not perform this operation on the site collection
http://abc.com. To add a URL for this site collection add a URL to the root host-named site collection at http://abc.com. At line:1 char:1