This is a great topic to cover in an e-book. I have been looking all over the internet to find this type of information with very little luck. Any general graphic creation/resizing/copying and reprinting information is what is needed. I have Paint Shop Pro, but I would assume that general techniques are easily transferable.
One topic of interest is making a copy of old decals and cleaning them up so they look "new". A second is resizing a set of decals to use on a larger or smaller scale model.
Thanks for thinking of this as there is very little real usable information on this topic.