Consider the neurological danger of visualizing yourself as (e.g. hitler) repeatedly over and over. The exercise mentioned above is one of neurological conditioning (anpassen in german). You are training your neural pathways to take on a certain form of thought pattern. If you pick (e.g.) hitler as your mould, then you are training yourself as hitler. That's what the danger is with such a practice.

Therefore, you must be careful and wise about what neurological mould you are seeking to "impersonate" with your practice, since you would be creating new habits and neural pathways in practice.

I'm not an expert on this topic, but I can use my common sense to figure that out.