has anyone here had experience with modifying DNS records through Yahoo Small Business?
The only two options it presents is "A/CNAME records" and "MX Records".
How would I go about setting the TXT records for Sender ID and DomainKey?
It's our understanding that Yahoo hosting doesn't allow you to add TXT records unfortunately. It's doubly sad since they helped come up with DomainKeys. You might want to try contacting them and see if they'd be willing to add them for you (sometimes they are, sometimes not).
Edit: is an alternative to register an "offersclientname.com" domain, set that up on our own servers? We would then have control over the DNS of that new domain.
I have the same issue. Did you ever get an answer form Yahoo?