Using profiles (as little as possible) and execution phase you may achieve what you want for plugins that do not handle the skip property:
Plugin configuration:
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>rpm-maven-plugin</artifactId>
<executions>
<execution>
<phase>${rpmPackagePhase}</phase>
<id>generate-rpm</id>
<goals>
<goal>rpm</goal>
</goals>
</execution>
</executions>
<configuration>
...
</configuration>
</plugin>
Profile configuration:
<profiles>
<profile>
<id>default</id>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<properties>
<rpmPackagePhase>none</rpmPackagePhase>
</properties>
</profile>
<profile>
<id>rpmPackage</id>
<activation>
<property>
<name>rpm.package</name>
<value>true</value>
</property>
</activation>
<properties>
<rpmPackagePhase>package</rpmPackagePhase>
</properties>
</profile>
</profiles>
Invocation:
mvn package -Drpm.package=true [...]