Oh, I don’t mean to say they are the same. It’s just that the nuance is hard to translate. So what intention or goal would 手始めにと express? 七罪 wanted sneaking into 士道’s room to be a beginning?社長にと is no different from 社長に? Well, then 手始めにと and 手始めに are all the same. The formers are more characterised with the intention of the speaker.