Adiyen’s have seen few non-brahmins wearing Yagnopavitham permanently. It doesn’t stop there. Adiyen have seen them doing Thrikala sandhyavandhanam as well and they change their poonal whenever it is supposed to be changed (few example: after hair cut, after any theetu etc..)
As we hear in Upanyasas of Sri U.Ve. Velukkudi Krishnan Swami and many others, people those belongs to three varnas (Brahmanas, Kshatriyas & Vaisyas) have to wear poonal always and they need to nithyakarmas as per their varnashrama dharma. For the people belonging to remaining one Varna, they need to wear poonal during Suba and pithru karyangal. So in general poonal is common for Sanathana dharmis.
Adiyen also noticed lot of people including non-brahmins doing Amavasya tharpanam.This can be seen every Amavasya at Nathikari or Theppakulam.