Using the "new ProjectTemplate" wizard I got something like:

@TemplateRegistration(...,
    iconBase = "org/metawb/template/project/quester/Quester.png",
    ...

Here the icon was copied by the wizard.
The app has a module with the icons used by the project, along with spi/api
defs and such. I decided to change the @Temp*Reg* to reference the icon

I tried
        iconBase = Icons.quester,

which is OK in the editor, but when I compile I get

    C:\a\src\wb-dev\wb\QuesterTemplate\src\org\metawb\template\project\quester\QuesterWizardIterator.java:56: error: Cannot find resource org/metawb/ui/resources/blackhole-icon.png
    @TemplateRegistration(folder = "Project/Metaphysical Workbench",
    warning: No processor claimed any of these annotations: org.netbeans.api.templates.TemplateRegistration


So I tried
        iconBase = "nbres:/"+Icons.quester,

and in the editor the error badge had an error

        Cannot find resource: nbres:/org/...png

and going ahead and compiling gave

    An annotation processor threw an uncaught exception.
    Consult the following stack trace for details.
    java.lang.IllegalArgumentException: Invalid relative name: nbres:/org/metawb/ui/resources/blackhole-icon.png
            at com.sun.tools.javac.file.JavacFileManager.getFileForInput(JavacFileManager.java:680)