If you want to publish content compatible with Level Up: Advanced 5th Edition, you can. You don’t even need to ask permission; you can simply use the Open Game License or the Creative Commons license. However, if you let us know, we’d love to hear about your products!
Of course, all 5E material is compatible with Level Up. But if you plan to produce material which takes advantage of the new features of the Level Up system, we provide a free compatibility logo.