since it was not possible to correctly convert multiplayer worlds or really big worlds with the IndustrialUpgrade converter, I decided to code a converter myself. Used it for my own server and it worked fine, so I wanted to share it with you I don't know if someone needs this thing, though
Extract the files from the .zip and execute the .exe. You can select the world folder by directly typing it or you can get it from the clipboard. To do this copy the location (with ctrl + c from your windows explorer for example) and enter v as the location in the converter. You can also change which blocks/items should be converted, just edit the mapping.txt. Try out the mapping_fun.txt, it will make your map shiny But do a backup first
About the Source:
You can also download the source code of the converter, if you want to edit it or add features. But please don't flame my code, i'm quite a noob in c#
Thanks to the author of Substrate, without your library the converter wouldn't have been possible. And thanks to linx_, who gave me the idea to make a converter myself.