Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
I am afraid your requirement is not possible.
Please note that while creating a domain in Azure, the name servers assigned to you are not unique to your domain (there is no 1:1 mapping).
These nameservers may be mapped to other domains in Azure as well.
And this makes sense, as the DNS resolution is provided by the Azure Architecture to various domains and the name servers belong to Azure.
So, customizing them is not something that can be done.
Should there be any follow-up questions or concerns, please let us know and we shall try to address them.
Cheers,
Kapil.