A few quetions on metta
As I understand things: Metta-meditation is not "magic", not something like "positive voodoo". In the first instance it is a training for you and your ability for loving kindness.
Based on this it is also a stepwise training: you start with simple ones (loving kindness with yourself, your mama, your spouse, your best friend). After you have some fluent experience you change the subject to more neutral persons, and then even to some people you dislike (or you think they dislike you), or to rivals.
The effect of the training - if successful for you : then your new way of impulses might have effects to the world...