Personally, even with permission from an owner to do things with their horse, training shouldn't be undertaken by someone who is not going to be consistently using the horse. I wouldn't allow someone to come along to my horse who has little training and start doing things they want to... but rather listen to the owner and follow their methods - if that situation arose. I personally as a horse owner wouldn't allow another person to train my horse unless hired to. It's too risky to install bad habits - not pointing negatively at yourself, as I admire your effort to learn more, not to mention even as owners ourselves we make mistakes! - and the relationship may turn sour if the horse reacts to something you have taught poorly.
I'd suggest you just continue working with the horse/donkey, and if they offer a chance to work with the horse under supervision, take it!
All the best, and again, not trying to be mean, but realistic.
♥ Seoul Searchin' for the Lovebug ♥