I agree with everyone else that I only found out about this by accident and good fortune. I don't imagine many of us spend our time checking all the latest legislation to see if there is any deer related info in there and, of course, there is no reason to check the deer seasons on the BASC site if you we not actually made aware that they had changed.
Perhaps they should have written to everyone in NI with a rifle conditioned for deer? Apart from that I really don't know how you get the word around and especially to people who might be less than receptive to paperwork and the like.
As ksb says I haven't managed to make it out much myself recently and the time up until the end of February isn't looking great for me either so the extra few days will be most useful.