One can find the Universal Norms on the Liturgical Year and the General Roman Calendar here. One can find the 1917 Code of Canon Law here.
Interestingly, the Universal Norms incorporate the transfer of certain feasts, including the Epiphany, to the following Sunday when not observed as distinct holydays of obligation. Thus, it would appear that one need not argue how much of a feast gets transferred or suppressed when the episcopal conference suppresses (or transfers) the obligation to hear Mass: the move to Sunday is part of the definition of the feast.
So this coming Friday really isn't, for Code of Canon Law purposes, the feast of the Epiphany in any sense, outside, perhaps, of a personal parish or (more certainly) a place where it remains a holyday of obligation.
This is a followup of sorts to an older post, here.