Start by putting the highlighted elements below in the POM of the application module:
Then switch to the Files window and, in the application module, create the above folder structure, i.e., "src/main/resources". In the "resources" folder you created, copy the "netbeans.conf" file from the NetBeans IDE installation directory (specifically, find it in the "etc" folder) and then change the name of the file to "my.conf".
In the "default_options" key, which is in the "netbeans.conf" file that you copied, add this value:
In other words, your "default_options" key is now something like this:
default_options="--laf com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel -J-Xms48m -J-Xmx512m -J-XX:MaxPermSize=240m "
Then run "Clean" on the parent module. Now run the application module. Hurray, you now have Nimbus:
Plus, note that you don't only have Nimbus while you're developing: your custom conf file now replaces the default template that would otherwise have been copied into your final application. You can now, for example, specify the JDK that will be used, as well as the memory settings, in your custom conf file, in the knowledge that those settings will be the same as those that the end users will end up with when you distribute the application to them.