I just uploaded a change at thisREST.sh. This change will allow to load ROOT, Geant4 and Garfield with this unique script.
The change makes sense because a compiled REST is linked to the ROOT that was used to compile it, and it should only be used with that ROOT compiled version.
Therefore, the bash script where we define ROOT, Geant4 and Garfield will be reduced to one line where we source /path/to/install/thisREST.sh.