Will it be rewarding for me to have my ears pierced and wear earrings as a man, if I believe it to be a sunnah of Prophet (s) as I have heard that he had the ears of Imam Hassan and Hussain pierced?
Bismihi ta'ala
No, it will not be rewarding. It could be haram as well, as in most, if not all Muslim societies this is unacceptable and socially inappropriate. In our Islamic law, it is called "libas al-shuhrah", which means dressing or wearing something that will invite criticism, negative comments, accusations, or ruining of reputation.
In general, a male wearing earrings does definitely fall under the category of libas al-shuhrah, which means it would be haram.
If it is confirmed that the Imam (a.s.) did have his ear pierced as a child, it does not mean he wore earrings, or kept on wearing it as an adult. We do not have any evidence for that.
And, even if it was done then, for argument sake, it might have been something common then, like men having kohl on their eyes as well, but now, it is uncommon and unpracticed, especially among religious people.
And Allah knows best.