In DEVONthink 3.x, (assuming the extra script isn’t installed)…
- Open DEVONthink’s Scripts menu > More Scripts.
- Install the Fix Hidden Prefs script.
- Select Scripts menu > Tabs > Open Hidden Preferences and a window will appear with DEVONthink’s hidden preferences.
- Locate the desired preference and click the On/Off link on the desired option.
Obviously, only steps 3 and 4 would be used going forward.
PS: While not always necessary, quitting and relaunching DEVONthink after changing a hidden preference is a good idea.