I don't think there are any sew-on or iron-on patches that are addons, all you could do is take one off a damaged bag and attach it somehow on to the replacement bag...
As for adding a long zip, the usual method is to cut out the seam that runs up the back of the bag and then stitch in a long zip, and then cut out the scraper pocket and stitch that zip shut, but personally I'd just extend the scraper pocket cutout ad put a long zip in there, so instead of two zips, you have one at an angle, but it's up to you how you do it... 
