Is it possible to make @IBDesignable override Interface Builder values?

I have created new IBInspectable as testFonts :

import UIKit

@IBDesignable

class CustomButton: UIButton {
    override init(frame: CGRect) {
        super.init(frame: frame)
        self.customInit()
    }

    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.customInit()
    }

    func customInit () {
        titleLabel?.font = UIFont.systemFontOfSize(20)
    }

    convenience init() {
        self.init(frame:CGRectZero)
        self.customInit()
    }

    override func awakeFromNib() {
        super.awakeFromNib()
        self.customInit()
    }

    override func prepareForInterfaceBuilder() {
        super.prepareForInterfaceBuilder()
        self.customInit()
    }
}

Hope it helps you :)

This is working for me.