Apache Geronimo provides a couple of configuration files where you can edit some of the parameters before starting the server. For instance, you can change the port numbers the server uses by updating the config-substitutions.properties file located in the <geronimo_home>/var/config/ directory. If you need to substitute one module with another you can use the artifact-aliases.properties or the client-artifact-aliases.properties files also available in the <geronimo_home>/var/config/ directory. In addition, you might also want to change the default user name and password and/or user groups. The files available in the <geronimo_home>/var/security/ directory allow you to make these changes.
Additional configuration changes can be made on the config.xml file available in the <geronimo_home>/var/config/ directory.