In my research for a timeline, I came upon the Malagasy Protectorate, which was a British protectorate in Madagascar 1882-1897. The British gave it to the French in exchange for France giving up their claims in Zanzibar.
Let us suppose that the POD is that the British value Malagasy over Zanzibar, why is not relevant. With the only claims on Zanzibar now being Germany and France, what might France offer to Germany in exchange for control over Zanzibar? I was thinking New Caledonia or Djibouti, but I don't know exactly how France ranked its colonies in value.