strictly followed it must be.

Paraphrasing Sri Ramanuja, Sri Desikan says that while performing any of these kainkaryams, one has to stay within the parameters prescribed by the shastras, and anything beyond or in contravention of the shastras can’t be classified as kainkaryam. This is borne out by the Gita slOka, which lays down that anybody contravening the edicts of the Vedas and smritis is a betrayer of the Lord, and ceases to be a Sri
Vaishnava. –

“Shruti: Smriti: mamaiva AgyA 
YastAm ullanghya varttatE 
AgyAchhEdi mama drOhi
Mama bhaktOpi na Vaishnava : «