Most of optical stores would be unwilling to add anti-glare coating on your present lenses, cuz the costing would bu much higher than manufacture a new lens with anti-glare coatings. So if you want a pair with anti-glare coating, it is suggested to have a new pair with the anti-glare coating lenses.
Of course you can. You can take your glasses back to your optician where you bought your glasses. Their lab will add the anti-glare coating on your lenses. But it may be costly. You can contact your optician to determine whether they are willing to do it for you.