You can now transfer your Flickr account between two different Yahoo! IDs. We’ve added links to the transfer tool on your account preferences page.
If you already use a Yahoo! ID to sign in to Flickr and want to switch to using a different Yahoo! ID, go here: www.flickr.com/account/transfer
(If you still have an “old skool” flickr.com account, you should still use the merge process at: www.flickr.com/account/associate)
For help with this tool, please see the official thread in the forums.