Some time ago there was a message posted to the fedora-config-list about a new package management tool: http://fedora.redhat.com/projects/config-tools/specs/redhat-config-packages
I believe such a tool may be necessary in order to do any shuffling of packages between Core and Extras (especially from Core to Extras).
That tool exists for some time. It's called system-config-packages lately. The downside is that it simply doesn't do all that yet.