To perform mental puja (manasika puja) initiation (upadesha) from your own Guru is not required.
One should know the procedure to perform this Puja. Anyone who explains this procedure to you is your Guru. You need to get the right instructions for this and not just do it as you wish. There is a prescribed procedure. You should either read it in the books, or take instructions from one who is experienced in it, or from your Guru.
I’m telling now that all present here have permission to do Manasika Puja. The Upadesha is done! This is not an Upadesha that is to be told secretly in one’s ear!
Once again I re-iterate, it is not about eligibility, it is about knowing the right way to do it.
To answer your second question- All rules applicable for the Vratas (rituals) are also applicable for Manasika Puja. One must follow all the stipulated rules.
**There is no Vrata (austerity) without rules. Without truth, there is no penance. Without cleanliness, there is no worship.
Cleanliness is essential. Penance refers to discipline, sincerity. You cannot get up in the middle of a puja, eat a Vada and come back to resume your puja. You cannot go to the bathroom in the middle of a puja. This is not puja. There is no discipline or cleanliness here. Dharma means being clean, being sincere, being truthful and having compassion towards all beings.
One who has these four qualities is eligible to perform Puja. Otherwise, Puja just becomes a mechanical act. You will not gain any merit. It is only an exertion, exercise!
(Q&A Session 19 Mar 2017)