When I got my first grey, Ana Grey, I asked that she not be clipped. Well the breeder did it anyway. Ana Grey was her bird not mine. The breeder's fear (am sure) was that Ana Grey would fly away as I was a new parrot owner and didn't know any better. The breeder would not take any money until she had met me. I will say that Ana Grey was well loved and is fearless thanks to her loving breeder. Would I have signed a contract saying I would not clip my new companion? No, I could not honestly do that... because once she was mine it was then my choice.
Would I never clip my birds? I can't guarantee that because things change... so I never say never. I do have my three parrots microchipped as I do fear greatly that they will venture outdoors without me. It is my biggest fear - That one or all will get out the door and fly around in the amazing excitement and when they land wonder why "mama" doesn't come get them now because - I'm tired and hungry and Mama always takes care of us. Where is she!
Back to the topic. You can put anything you want in a contract..... you just have to get someone/other party to sign it.