Well you can do that by first getting a reference to the ParagraphStyle, and then settings the properties. Here's the ParagraphStyle documentation.
Here is some code that gets a reference to a paragraph style and then sets some of its properties:
var doc = app.activeDocument,
myParagraphStyle = doc.paragraphStyles.itemByName('My Paragraph Style');
// example of changing some properties
myParagraphStyle.properties = {
composer: 'Adobe Paragraph Composer',
characterDirection: CharacterDirectionOptions.RIGHT_TO_LEFT_DIRECTION,
hypenation: false,
pointSize: 11,
}
/*
Properties of ParagraphStyle:
• alignToBaseline
• allowArbitraryHyphenation
• appliedFont
• appliedLanguage
• appliedNumberingList
• autoLeading
• autoTcy
• autoTcyIncludeRoman
• balanceRaggedLines
• basedOn
• baselineShift
• bulletChar
• bulletsAlignment
• bulletsAndNumberingListType
• bulletsCharacterStyle
• bulletsTextAfter
• bunriKinshi
• capitalization
• characterAlignment
• characterDirection
• characterRotation
• cjkGridTracking
• composer
• designAxes
• desiredGlyphScaling
• desiredLetterSpacing
• desiredWordSpacing
• diacriticPosition
• digitsType
• dropCapCharacters
• dropCapLines
• dropCapStyle
• dropcapDetail
• emitCss
• endJoin
• eventListeners
• events
• fillColor
• fillTint
• firstLineIndent
• fontStyle
• glyphForm
• gradientFillAngle
• gradientFillLength
• gradientFillStart
• gradientStrokeAngle
• gradientStrokeLength
• gradientStrokeStart
• gridAlignFirstLineOnly
• gridAlignment
• gridGyoudori
• horizontalScale
• hyphenWeight
• hyphenateAcrossColumns
• hyphenateAfterFirst
• hyphenateBeforeLast
• hyphenateCapitalizedWords
• hyphenateLadderLimit
• hyphenateLastWord
• hyphenateWordsLongerThan
• hyphenation
• hyphenationZone
• ignoreEdgeAlignment
• imported
• includeClass
• jidori
• justification
• kashidas
• keepAllLinesTogether
• keepFirstLines
• keepLastLines
• keepLinesTogether
• keepRuleAboveInFrame
• keepWithNext
• keepWithPrevious
• kentenAlignment
• kentenCharacterSet
• kentenCustomCharacter
• kentenFillColor
• kentenFont
• kentenFontSize
• kentenFontStyle
• kentenKind
• kentenOverprintFill
• kentenOverprintStroke
• kentenPlacement
• kentenPosition
• kentenStrokeColor
• kentenStrokeTint
• kentenTint
• kentenWeight
• kentenXScale
• kentenYScale
• kerningMethod
• keyboardDirection
• kinsokuHangType
• kinsokuSet
• kinsokuType
• label
• lastLineIndent
• leading
• leadingAki
• leadingModel
• leftIndent
• ligatures
• maximumGlyphScaling
• maximumLetterSpacing
• maximumWordSpacing
• mergeConsecutiveParaBorders
• minimumGlyphScaling
• minimumLetterSpacing
• minimumWordSpacing
• miterLimit
• mojikumi
• name
• nestedGrepStyles
• nestedLineStyles
• nestedStyles
• nextStyle
• noBreak
• numberingAlignment
• numberingApplyRestartPolicy
• numberingCharacterStyle
• numberingContinue
• numberingExpression
• numberingFormat
• numberingLevel
• numberingRestartPolicies
• numberingStartAt
• otfContextualAlternate
• otfDiscretionaryLigature
• otfFigureStyle
• otfFraction
• otfHVKana
• otfHistorical
• otfJustificationAlternate
• otfLocale
• otfMark
• otfOrdinal
• otfOverlapSwash
• otfProportionalMetrics
• otfRomanItalics
• otfSlashedZero
• otfStretchedAlternate
• otfStylisticAlternate
• otfStylisticSets
• otfSwash
• otfTitling
• overprintFill
• overprintStroke
• paragraphBorderBottomLeftCornerOption
• paragraphBorderBottomLeftCornerRadius
• paragraphBorderBottomLineWeight
• paragraphBorderBottomOffset
• paragraphBorderBottomOrigin
• paragraphBorderBottomRightCornerOption
• paragraphBorderBottomRightCornerRadius
• paragraphBorderColor
• paragraphBorderDisplayIfSplits
• paragraphBorderGapColor
• paragraphBorderGapOverprint
• paragraphBorderGapTint
• paragraphBorderLeftLineWeight
• paragraphBorderLeftOffset
• paragraphBorderOn
• paragraphBorderOverprint
• paragraphBorderRightLineWeight
• paragraphBorderRightOffset
• paragraphBorderStrokeEndCap
• paragraphBorderStrokeEndJoin
• paragraphBorderTint
• paragraphBorderTopLeftCornerOption
• paragraphBorderTopLeftCornerRadius
• paragraphBorderTopLineWeight
• paragraphBorderTopOffset
• paragraphBorderTopOrigin
• paragraphBorderTopRightCornerOption
• paragraphBorderTopRightCornerRadius
• paragraphBorderType
• paragraphBorderWidth
• paragraphDirection
• paragraphGyoudori
• paragraphJustification
• paragraphKashidaWidth
• paragraphShadingBottomLeftCornerOption
• paragraphShadingBottomLeftCornerRadius
• paragraphShadingBottomOffset
• paragraphShadingBottomOrigin
• paragraphShadingBottomRightCornerOption
• paragraphShadingBottomRightCornerRadius
• paragraphShadingClipToFrame
• paragraphShadingColor
• paragraphShadingLeftOffset
• paragraphShadingOn
• paragraphShadingOverprint
• paragraphShadingRightOffset
• paragraphShadingSuppressPrinting
• paragraphShadingTint
• paragraphShadingTopLeftCornerOption
• paragraphShadingTopLeftCornerRadius
• paragraphShadingTopOffset
• paragraphShadingTopOrigin
• paragraphShadingTopRightCornerOption
• paragraphShadingTopRightCornerRadius
• paragraphShadingWidth
• pointSize
• position
• positionalForm
• preferences
• previewColor
• providerHyphenationStyle
• rensuuji
• rightIndent
• rotateSingleByteCharacters
• rubyAlignment
• rubyAutoAlign
• rubyAutoScaling
• rubyAutoTcyAutoScale
• rubyAutoTcyDigits
• rubyAutoTcyIncludeRoman
• rubyFill
• rubyFont
• rubyFontSize
• rubyFontStyle
• rubyOpenTypePro
• rubyOverhang
• rubyOverprintFill
• rubyOverprintStroke
• rubyParentOverhangAmount
• rubyParentScalingPercent
• rubyParentSpacing
• rubyPosition
• rubyStroke
• rubyStrokeTint
• rubyTint
• rubyType
• rubyWeight
• rubyXOffset
• rubyXScale
• rubyYOffset
• rubyYScale
• ruleAbove
• ruleAboveColor
• ruleAboveGapColor
• ruleAboveGapOverprint
• ruleAboveGapTint
• ruleAboveLeftIndent
• ruleAboveLineWeight
• ruleAboveOffset
• ruleAboveOverprint
• ruleAboveRightIndent
• ruleAboveTint
• ruleAboveType
• ruleAboveWidth
• ruleBelow
• ruleBelowColor
• ruleBelowGapColor
• ruleBelowGapOverprint
• ruleBelowGapTint
• ruleBelowLeftIndent
• ruleBelowLineWeight
• ruleBelowOffset
• ruleBelowOverprint
• ruleBelowRightIndent
• ruleBelowTint
• ruleBelowType
• ruleBelowWidth
• sameParaStyleSpacing
• scaleAffectsLineHeight
• shataiAdjustRotation
• shataiAdjustTsume
• shataiDegreeAngle
• shataiMagnification
• singleWordJustification
• skew
• spaceAfter
• spaceBefore
• spanColumnMinSpaceAfter
• spanColumnMinSpaceBefore
• spanColumnType
• spanSplitColumnCount
• splitColumnInsideGutter
• splitColumnOutsideGutter
• splitDocument
• startParagraph
• strikeThroughColor
• strikeThroughGapColor
• strikeThroughGapOverprint
• strikeThroughGapTint
• strikeThroughOffset
• strikeThroughOverprint
• strikeThroughTint
• strikeThroughType
• strikeThroughWeight
• strikeThru
• strokeAlignment
• strokeColor
• strokeTint
• strokeWeight
• styleExportTagMaps
• styleUniqueId
• tabList
• tabStops
• tatechuyoko
• tatechuyokoXOffset
• tatechuyokoYOffset
• tracking
• trailingAki
• treatIdeographicSpaceAsSpace
• tsume
• underline
• underlineColor
• underlineGapColor
• underlineGapOverprint
• underlineGapTint
• underlineOffset
• underlineOverprint
• underlineTint
• underlineType
• underlineWeight
• verticalScale
• warichu
• warichuAlignment
• warichuCharsAfterBreak
• warichuCharsBeforeBreak
• warichuLineSpacing
• warichuLines
• warichuSize
• xOffsetDiacritic
• yOffsetDiacritic
*/
Hope that gives you something to work with.
- Mark