What do you expect to achieve? i.e. define 'customized' a little and say what device you're using. You cannot do much with modern garmin charts/maps really because of the proprietary .img format. If you are wanting to load just a portion of a chart to a device, that's not practically possible because of the problem that Vision charts are supplied as fully compiled images. Trying to 'split' such an image will result in loss of features and render it practically useless on a chartplotter in 'real world' application. Just guessing a little there as to what you're wanting to do. Post again with more info if that hasn't answered you.