if I already have a bibsonomy account, how can I switch to openID?
More generall, the OpenID support in BibSonomy is currently pretty simple: one can register with OpenID and login - that's it.
It is not possible, to change an OpenID or to migrate an existing account from "internal" login to OpenID login (or the other way round). Some systems also support several OpenIDs per account, this would be nice but not necessary.
Please keep in mind that changing or adding an OpenID always requires to check if the OpenID is valid.