I would use the record macro feature under View-->Macros to do this. Start recording and make the changes. The following recorded macro should point you in the right direction:
    With ActiveDocument.Styles("Table Grid").Table.Condition(wdSECell). _        ParagraphFormat
        .LeftIndent = InchesToPoints(0)
        .RightIndent = InchesToPoints(0)
        .SpaceBefore = 0
        .SpaceBeforeAuto = False
        .SpaceAfter = 0
        .SpaceAfterAuto = False
        .LineSpacingRule = wdLineSpaceSingle
        .Alignment = wdAlignParagraphLeft
        .WidowControl = True
        .KeepWithNext = False
        .KeepTogether = False
        .PageBreakBefore = False
        .NoLineNumber = False
        .Hyphenation = True
        .FirstLineIndent = InchesToPoints(0)
        .OutlineLevel = wdOutlineLevelBodyText
        .CharacterUnitLeftIndent = 0
        .CharacterUnitRightIndent = 0
        .CharacterUnitFirstLineIndent = 0
        .LineUnitBefore = 0
        .LineUnitAfter = 0
        .MirrorIndents = False
        .TextboxTightWrap = wdTightNone
        .CollapsedByDefault = False
    End With