During the game, press TAB and type

"SET PLYR.DS9_[character name here] HEALTH 999"

When I say [character name here], you must put in either SISKO, SISKOEVA (if he is wearing a spacesuit), KIRA, KIRAEVA (if she is wearing a spacesuit), KIRACARD (you'll know when to use this late in the game), WORF, or WORFEVA (if he is wearing a spacesuit). The actual number "9999" can be any positive number up to 9999999999 or so.