Yeah no need. If you are keeping the same motherboard you should never need to format, it's the only part that really should have a clean install when replaced (unless replaced with the exact same model).
You might want to be sure your Windows license is tied to your Microsoft account so your license will transfer over.
Larry
Lol, not for a CPU upgrade. You can change a few parts without triggering any activation issues.
Unless multiple different parts have been upgraded in the past a CPU upgrade will not be an issue with activation and I don't think even then.