any characteristic of the argonians can be changed in the presence of the hist (see morphological changes from TES III-V) but while argonians (and their eggs) are particularly 'maleable' the hist can change about anything in black marsh.

the question here is what the characteristics the hist made to facilitate reproduction far afield, the existence of argonians that had never been to black marsh is established but the difficulty/danger associated isn't elaborated. it's possible grains, even heaps of argonians might've lived so disconnected from the hist that they might still possess traits from TES III like reverse legs---populations in morrowind for example.