Hi Adrian,
Both of these links are customised via the order form template files:
* The Explore Packages now button is located in domainregister.tpl around line 273.
* The "No Hosting! Click to Add" link is located in configuredomains.tpl around line 64.
Line numbers are accurate at the time of writing.
More information is available in our documentation: https://docs.whmcs.com/Order_Form_Templates