If you want to create an addon we strongly recommend to read the relevant tutorial: How to create AddOns for QuantumATK. There is no special restriction for addon creation in general. Synopsys QuantumATK Team creates addons in a permanent basis but also any other QuantumATK user has the permission to create addons either for a personal use or for wider usage (expanding QuantumATK’s capabilities) after Synopsys’s consent. For more details read the ~/QuantumATK/QuantumATK-V/lib/site-packages/AddOns/LICENSE file (where V denotes QuantumATK version). Also you can get more details in How to Create AddOns tutorial. This tutorial just gives the general framework through some examples since, obviously, the design of an addon depends on its purpose.