This will be good news for all the modelers & designers on Shapeways. We have just released what is probably our most requested feature ever. We call it versioning and it will make your world a happier place.
If you look at one of your own models you can now see the "update model" button beneath it. If you click on that model you can upload a new file to replace the existing one. The new file will have the same URL as the previous one and all your comments, ratings, description etc. will be kept.
In this way incremental improvements to a model & design iterations can be kept with minimal hassle for the community member. Have fun trying it out. The line to help build a momument to Arno and his coder buddies starts to my right.