You will actually set this up logged in as a reseller (like Techno stated), Settings >> Products >> Domain Registration >> WHOIS format.
This will change it across your WHOLE reseller account :
Compulsary Tags (You must have these tags somewhere in your format):
<#=domainname#>, <#=expirydate#>, <#=creationdate#>, <#=nameserver#>, <#=registrantcontactdetails#>, <#=administrativecontactdetails#>, <#=technicalcontactdetails#>, <#=legalnote#>
Optional Additional Tags (These tags may be used by you additionally to display more information):
<#=whoisbox#>,
<#=registrationserviceprovider#>,<#=billingcontactdetails#>
You are allowed to put in whatever you want remember

SO you could have for instance have at the top :
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Registration service provided by WPAHOST
Find us on the web at : http://Wpahost.com
Domain from $7.99, monthly special keep your eyes peeled
Contact us at support@mydomain.com or by phone +6221.99900771
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And then put everything else underneath that is compulsary
