Thank you for the request, we will take it into account. However we don't plan to change our policy of updating libraries in near future. We add a lot of new components and fix known mistakes in every new version, it is much safer for us to overwrite existing files to prevent possible problems.
Thanks for the reply, Alex. I guess the answer, since it's relatively easy to import parts from one library into another, is for me to put all the parts I create (components and patterns) in my own private libraries to begin with, and then import them into other libraries as appropriate. That way, when I update my libraries from the DipTrace website, I will still have all the parts I've built for myself. I suppose that works also for sharing parts that I've built with the rest of the DipTrace community--having them in private libraries makes it easy to insure that I'm posting just my own contribution. It's always good to be cautious about parts you get from unknown users anyway. You wouldn't necessarily want user-contributed parts to be in the "official" libraries. There can be errors from honest mistakes, as well as the possibility of malicious postings.
I do agree with TechGuy's comment that extensive, accurate libraries are one of the keys to having an electronics CAD program widely adopted.