To override the classes that would run on the ATG server, one simply copies your new classes into the locallib directory under the correct directory which corresponds to the package. To learn more, Modifying the Environment Settings.

However on an ATG Dynamo 4.5.1 server running on FreeBSD I found the locallib classes were not loading no matter how many times I restarted the ATG Dynamo server. I realized finally by accident that the reason these classes weren’t being loaded was because another ATG Dynamo server was running and because of this the Java process was not releasing its understanding of the CLASSPATH. Only after killing the second ATG Dynamo server process was I finally able to get the ATG Dynamo server to load the new classes.