Resolving: MNG-163 Use MavenProject.addResource(..) and .addTestResource(..) to perform this function. I've built a BuildOverlay to insulate the interpolated, initialized Model's Build instance from runtime changes to these, in a similar fashion to addCompileSourceRoots(..), because I wanted to preserve some compat with plugins using ${project.build.resources}.
maven/components/trunk/maven-plugins/maven-resources-plugin/src/main/java/org/apache/maven/plugin/resources/ResourcesMojo.java
maven/components/trunk/maven-project/src/main/java/org/apache/maven/project/overlay/