@Manfred Moser: Yes you are right. After searching on net I got the same trick.
A more detailed answer is:
1) Create a new repository.
2) Add that repository to the a repository group
3) You can also change the repository resolving order
Sample Setting XML is:
{
<mirrors>
<mirror>
<!--This sends everything else to /public -->
<id>MyRepo</id>
<mirrorOf>*</mirrorOf>
<url>http://localhost:port/nexus/content/groups/public</url>
</mirror>
</mirrors>
<profiles>
<profile>
<id>MyRepo</id>
<!--Enable snapshots for the built in central repo to direct -->
<!--all requests to MyRepo via the mirror -->
<repositories>
<repository>
<id>central</id>
<url>http://central</url>
<releases><enabled>true</enabled></releases>
<snapshots><enabled>true</enabled></snapshots>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>central</id>
<url>http://central</url>
<releases><enabled>true</enabled></releases>
<snapshots><enabled>true</enabled></snapshots>
</pluginRepository>
</pluginRepositories>
</profile>
</profiles>
<activeProfiles>
<activeProfile>MyRepo</activeProfile>
</activeProfiles>
</settings>
}