Yes its possible!! When I first got my OTTB as a 3 year old (now 6), he was terrified of EVERYTHING at shows. The jump judges, the chairs they sat in, the extra jump poles from higher levels on the ground, the water buckets in horses' pastures, the other BIGGER prelim jumps on the XC course. Now, although 3 years later, he is still green and a little hesitant with new things but has gotten much bolder. He spooks at things he has never seen before but the key is to get them out as much as possible. Take him somewhere almost every week if you can. Show him EVERYTHING. It may take time but yes it is possible! My sister's event horse who is worth $40,000 or more has competed through intermediate level eventing very successfully BUT on a normal trail ride and at home he is quite spooky. We went on a trail ride the other day together and he spooked at more stuff than my greenie! But at shows, he is focused and knows his job and doesn't have time to think about spookign.