I just released a new version of the Maven RPM builder. Version 0.6.0 allows one to influence the way the RPM release information is generated during a SNAPSHOT build (also see issue #2).
While the default behavior is still the same, it is now possible to specify the snapshotBuildId, which will then be added as release suffix instead of the current timestamp. Setting forceRelease can be used to disable the SNAPSHOT specific logic altogether and just use the provided release information.