It is a reg change, but there's a better way to change it rather than messign with the registry directly. Besides, in some Unity versions the registry entry is an object guid...not friendly to enter.
Crack open DPT and select the appropriate directory monitor button (AD Monitor for E2K or Ex55 monitor for E55). Look for the properties...
NEWDITSLIST_ROOT
NEWLOCATION_ROOT
NEWMAILUSER_ROOT
You should be able to change the values there. DPT will write the correct value into the registry. If you're unfamiliar with DPT or how the DN should look, don't mess with this, let TAC assist.