VeriSign will not sell you a "root" or "CA" certificate that can sign other certificates (which is what Fiddler uses to intercept traffic). They will
sell you an "end-entity" or "server" certificate, which is used by a single server.
If you buy such a certificate and thus have its private key, then yes, you are able to use that certificate for that specific server. To do so, click Rules > Customize Rules > Scroll to OnBoot, and add the following
Having said that, this is generally not a very good idea, because it means that your super-sensitive private key is getting stored on a relatively low-trust developer machine. Generally, you should only ever install a publicly-trusted certificate on a protected and properly-configured front-end server.
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