Java Neophyte - question on best way to manage customization

My back ground is more on the DB side and I am definitely a beginner when it comes to Java.

That being the case I am trying to get some suggestions on the best way to manage some site specific customization.

In this case we have a requirement that all constraints follow a naming convention and the addNotNullConstraint does not support this functionality.

So as part of my learning experience I have made a custom copy of the liquibase code rel 1.9.  and expanded the java class to include this additional attribute. I then added the appropriate getter, setters, and a new constructor for when a constraint name is passed as a parameter.

While this is a good learning process, it will be a mess to maintain.

So what would be the suggestions on the correct approach in the design to extend liquibase to meet my site specific needs, while at the same time leaving the Open Source Objects unmodified to support future releases of liquibase.

Thanks Bruce