If you need the repackaged jar to have a different local name than the one defined by the artifactId attribute of the project, simply use the standard finalName as shown in the following example:

<project>
  ...
  <build>
    <finalName>my-app</finalName>
    <plugins>
      ...
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
        <executions>
          <execution>
            <id>repackage</id>
            <goals>
              <goal>repackage</goal>
            </goals>
          </execution>
        </executions>
        ...
      </plugin>
      ...
    </plugins>
    ...
  </build>
  ...
</project>

This configuration will generate the repackaged artifact in target/my-app.jar.