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SimDist can usually figure out how to manipulate these version tags into the format required for accessing the package's sources via cvs or download. The only exception to this currently is the HepPDT package. You should not change the version of this package, anyways. For other packages, it may be useful to override the defaults. For instance, selecting a different Geant4 version might be necessary. You can do this by editing the Geant4 version file at packages/geant4/VERSION. The Geant4 version string may also have a b instead of a p to designate beta versions.