Here is from Hernes guide:
I tried his method which worked on smaugfuss 1.9 and I tried kayles suggested method.
In either case it says exit added, but theres no door. Wierd.
If only 'redit exit (direction)' is specified, the exit will be removed.
The 'key' field is optional when specifying keywords. All other fields
are required previous to the field desired.
redit exit n 3001 - Creates an exit north to room 3001
redit exit n 3001 3 gate - Changes the exit n to have a closed "gate"
redit exit n 3001 3 15 gate - Changes the gate to allow a key (vnum 15)
redit exit n - Removes the north exit