Dunno if anyone has an easier or faster way, but for now, I load up the editor directly by creating an additional Doom 3 shortcut and adding “+ editor” as part of the target in the shortcut properties.
Starting Up the Editor
swelt
(swelt)
#3
Best shortcut should look something like this:
doom3 +editor +set r_fullscreen 0 +seta radiant_nameprefix yourname