you need to see the wiki page and modifying db by using :
config setprop KEY PROP VALUE [PROP VALUE]
example : to activate LearnAsSpam and set tag to [LearnedAsSpam]. (point represent a space)
config setprop LearnAsSpam status enabled tag '[LearnedAsSpam] '
(you see if you want a space betwin the tag and the subject you need to place your tag betwin ' ')