Since GEM modifies the GPL.exe, the only way to preserve your unmodified setup
is to copy/paste both versions into different folders ... these safety vaults
can even be inside your main GPL folder ... bring out whichever one you want to
play with.
Also check out Alison Hines's discussion of online usage of GEM
http://alison.simracing.com/gpl/gem.htm
Yr friend in the aether,
smogbike