the Yuuvis RAD system stores the mimetype that is given by the client. Only if the uploading client does not provide a mime type, or just provides application/octet-stream, the mime type is determined by a mapping of file extensions to mime type list, that is kept on server side.
By uploading content while providing the mime type, this mime type gets stored. For an api client it can be set by providing a 'Content-Type' http header. A browser sends (in most cases) the Content-Type header according to the OS settings. In windows it is possible to add a custom mimetype mapping in the CLASSES registry.
Example for WebAssembly files:
Windows Registry Editor Version 5.00
By importing this win registry entry on the client machine, a uploaded wasm file, will get the content type application/wasm.
The other way to solve this problem, is to adjust the server extension to mimetype mapping. This is done by editing the jas-systemmimetypes.xml file in the configuration folder. Advantage: No need to change an individual client - Disadvantage: Core-Service restart is necessary to get the configuration active. After Update/New installation this configuration has to be done again.
Hope this helps.