Hi Mike,
I would like to clarify with you the meaning of “partially redelegate” you referred to?
For Office 365 for Small Businesses users, after domain verification, they can no longer to manage DNS record by themselves after pointing name servers to Office 365 hosts. Beyond that, users can also verify your domain for Office 365 and continue to manage their domain’s DNS records.
The following articles for your reference:
Verify your domain and change name servers
Add your domain to Office 365 but continue to manage your domain's DNS records
If anything unclear, please feel free to post back.
Thanks,
Maggie Li