As adjectives the difference between atypical and customary
is that
atypical is not conforming to the normal type while
customary is agreeing with, or established by, custom; established by common usage; conventional; habitual.
As nouns the difference between atypical and customary
is that
atypical is (pharmacy) an atypical antipsychotic while
customary is a book containing laws and usages, or customs; a custumal.