Quoting PMuir from the Seam/WebBeans team:

the correct way to do this is to maintain a dependency graph, so that when you reload one EJB, you can reload all it dependencies, however you could easily end up with all ejbs being reloaded. Seam gets around this by making the user do this dependency management, and place only classes they are working on in hot-deploy. I believe JBoss MC can do this individual reloads of beans (as it controls the classloader completely).

source: http://www.seamframework.org/Community/ProperHotDeploymentAProposal

There is great interest in realizing complete hot-deployable EJB3 components in the JEE community.

There is a product called JavaRebel which just released version 2.0 but it does not support EJB3 hot deployment (completely, meaning add methods or changing signatures/params in existing methods) and no Seam plug-in is available.

JavaRebel supports changing EJBs including adding methods, fields and so on to classes. However we don't support at the moment in most cases changing EJB Local/Remote interfaces, as this usually requires a container postprocessing step.

source: http://www.theserverside.com/news/thread.tss?thread_id=54088

When is this going to become a reality with JBoss AS and Seam/WebBeans applications??