È possibile utilizzare NSAttributedString
di modificare il presente (Swift 4 esempio):
let title:String = "Your text"
let textParagraph:NSMutableParagraphStyle = NSMutableParagraphStyle()
textParagraph.lineSpacing = 10.0 /*this sets the space BETWEEN lines to 10points */
textParagraph.maximumLineHeight = 12.0/*this sets the MAXIMUM height of the lines to 12points */
let attribs = [NSAttributedStringKey.paragraphStyle:textParagraph]
let attrString:NSAttributedString = NSAttributedString.init(string: title, attributes: attribs)
titleTextField.attributedStringValue = attrString