Homebrew item property override

There are several things on an item (damage and range being the most prominent) that can't be adjusted.  The Homebrew system allows one to add to an item, but changing the item is basically impossible.  For example, if I wanted a shortbow that did 1d12+Str with a 120/360 range instead of 1d6+Dex 80/320, with the current system I'd just have to manage all that manually and remember that my shorbow is weird.