A close friend of mine, a Sri Vaishnava told me that he does not perform the Mahalaya Paksha Tharpana.
He informed me that , as an Iyengar belonging to Thengalai Sampradya, he does not do it as it is prohibited by Ramanucharya.
He told me that the other sect of Iyengars in Tamil Nadu, Vadagalai Iyengars perform the Pitru Paksha Tharpana.
As I am unable to find any authentic source on this, I am posting my views.
Those who know the subject well may quote with source.
In Hinduism there are two paths in terms of Lifestyle.
One is called Pravritti Marga and another Nivrutti Marga.
Pravrutti Marga is the leading of our daily lives , as normally do, by going after the sense objects.
Nivrutti Marga is renunciation of the sense objects.
Hinduism teaches how to live,taking into account the limitations and the frailties of Human Life including the desire to go after sensory objects for pleasure.
So Hinduism has devised the four stages of Life.
Brahmacharya, the young Celibate.
Gruhastha when one gets married begets children and goes about Life.
Vanaprastha,when one, after the son becomes capable managing the Family leaving the Family, either with or without wife to seek Reality either in the Forest or staying at Home in a detached way.
My friend quoted Visishtadvaita to support his view that one need not perform the Karmas,excepting Sandhyavanadan and Amavasya Tharpana as Sri Vaishnavism gives priority to surrender to Lord Vishnu and once one surrenders himself to God, one need not, should not perform Karma , including Pitru Paksha Tharpana.
He quoted the Sloka form the Bhagavad Gita, this is also called the Karna Mantra,,
Sarva Dharma Parijyasya Maameka Charanam Vraja,
Aham Thva Sarva Paapepyp0Mokshayisyami Maa sucha. Chapter 18
Leave all actions, and surrender only to Me.
I shall absolve you of all your sins and grant you Moksha’
I think my friend does not seem to have understood Krishna and this sloka is often misunderstood.
What Krishna says is that He shall grant Moksha and one need not perform any action(Karma) if one surrenders to Krishna.
The surrender , Krishna means a surrender is not a lip service but one of total Surrender,mind ,words and deeds.
By merely saying one has surrendered to Krishna does not mean total surrender.
Draupadi who wass a cousin of Krishna and an ardent devotee had to throw her arms up and pray Lord Krishna when Dhuchashana was stripping her.
Krishna did not pay heed to her earlier entreaties to save her when she held her hands to her saree: only when, she ,devoid of Ego , called out, leaving her hands off the saree, did Krishna rescue her modesty.
Such a devotion is very difficult to come by.
It needs years of practice ,Abhyasa and determination(vairagya)
This, I think we do not, posses at least I do not.
So the statement , presumably said by Ramanucharya, that one need not perform Karmas if one surrenders to Vishnu, is meant for evolved souls;such loved souls like Ramadasas,Ramakrishna Paramahamsa may and can follow this as they had lost Dehatma Buddhi, the attachment to Body.
We can not compare ourselves to these souls.
Again, while talking about Renunciation, Krishna says in the Bhagavad Gita, those who call the,selves Sanyasis , while their Minds are after sense objects, may appear so outwardly. are only Aashaadaboothis(hypocrites)
The determination to relinquish the fruits of action even at the mental level while performing the action is called renunciation.
With such a mindset one can even be in family Life, like Janaka, father of Sita.
Therefore the non-performance of Pitru Pksha , quoting some Acharya is contrary to Vedas and as such is incorrect as Pitru Yagnya is one of the most important and mandatory Yagnya for every one.