Why not just keep it simple, if the creator of a racing series/ server has identified a mod that they want to use for an event or entire series they should be able to contact the mod creator with a request to use the mod for a set period of time, 1 event/ 1 month/ 3 months/ 6 months/ 1 year. It can work with a simple tick box and all the mod creator has to do is approve or deny the request. If this is approved, the mod creator will then be locked out of deleting the mod/ making it private or updating the mod until that agreed time period has expired. Thereafter the mod creator could do what they like: delete/ update/ make private e.t.c. This way you have "buy in" from both the mod creator and the event creator.