bramhayagyanga pitrutarpanam
Sir,
Brahmayagyam is a part of our NityaKarma Ansuhtanam and has to be done without fail after Madhyanikam . AS regards the Pitru Tarpanam part of Brahmayagyam as you have rightly mentioned the same has to be performed only with water every day ( no black til is required ) .
As regards your question if pitru tarpana for vasu rudra aditya purushas can be done without til and with water in daily bramha yagnam ? - I would like to clarify that in our brahmayagyam part we just pray to our Pitrus as part of the pirtru tarpanam and the mantrams in Brahmayagyam cover only pitrus and not vasu rudra aditya purushas which are covered only in Amavasya , Sankramana and Grahana Tarpanams
As regards to your query regarding Varshabdigam , since Brahmayagyam is part of our daily ansuhtanams you can perfom the same after Brahmayagyam and the same is not dependant on any event , since our Shastra's clearly state that the only ritual which a Brahmin is permitted to perform even in case of a death in the family is Sandhyavndanam ( includes - Prataha , Madhyanikam , brahmayagyam and sayam sandhyavandanam) , hence you may continue to perform the same.
Regards
Narayan