Those who are not ordained to perform sandhyavandanam can chant the holy names of Bhagavan. One need not fret for not doing so as each of us are ordained by scriptures to perform austerities accordingly.
Though we do not possess the right to perform certain austerities yet there is no dearth in the fruits we derive. For example, women cannot perform duties that are ordained for men. Paricharakas cannot perform the duties assigned to a priest in a temple. It is better that we do the rituals assigned to us. You do not have to worry as you can go to a temple for worshipping Perumal and you can chant his divine names to alleviate from the sins.