How about new mime-types for custom files?

Hi! I’d like to get some more informations about registering new mime-types for my custom files I make in my game-applications. For example if I’d like to have sprites recognized as a new mime-type, say image/Sprite-png or image/Sprite-jpeg, and to get my application opening them as a known supported type, how can the OS be informed of that new mime-type ? Is there any mime-type-registry to update ?
For the moment I just get the extension name as the type, e.g. customModel.mc3 … <- this should be a bin/MC3-Model type. ???