Ouch, we should probably change that message for the time being unless someone wants to tackle merging accounts.
Some history ...
The old ACS 3.x system did include the (very useful) ability to merge accounts. When ACS 4 was developed, that and several other useful user management tools did not get re-implemented in the new framework.
Then Ars Digita embarked on their ACS Java rewrite, and work stopped on ACS 4.
That's when our project, originally meant to simply provide PostgreSQL support for Ars Digita's Oracle-based ACS toolkits, took over the entire Tcl-based ACS realm.
We're now just getting to the point where we're starting to pay attention to some of the serious shortcomings in the administration tools for users, groups, subsites etc. There's going to be substantial work done for OpenACS 4.7.
So ... I'd appreciate your filing a bug report describing this problem. Can't promise it will get addressed by 4.7. Of course ... if you want to dig in and try to figure out how to implement the feature we can certainly give you lots of advice and help!
