It is possible to put your properties in a file and make the name and location of the file a resource-ref of type URL in web.xml. The value of the resource is set in geronimo-web.xml.
Your web.xml will have the following entry:
<resource-ref>
<res-ref-name>configFileName</res-ref-name>
<res-type>java.net.URL</res-type>
</resource-ref>
In geronimo-web.xml you define the value for the configFileName
<name:resource-ref>
<name:ref-name>configFileName</name:ref-name>
<name:url>file:///etc/myConfigFile</name:url>
</name:resource-ref>
In java you have the following code to lookup the value:
initialContext = new InitialContext();
URL url = (URL) initialContext.lookup("java:comp/env/configFileName");
String configFileName = url.getPath();
Then you have to open the file and read whatever value is in there.
The result of all this is that you have the properties in a file on the filesystem. It will not be overwritten if you redeploy your application.