Hypothetically, if Death knights are unholy beings that can't get drunk normally...
Would blessing the booze with the Holy Light help bypass the unholy immunity?
I don't think that works. I mean, if you poured Holy Water into their mug of ale they would feel some sort of horrifying, searing pain I'm sure, but I don't think they'd get drunk.
I believe that the term 'living death knight' came from the second generation of paladins who essentially were fallen paladins who offered their service to the Scourge. The theme has passed on to the third generation of which we RP. The turning into a death knight does not involve death itself, but as a tool of the Lich King you would note be treated differently because you are alive for the moment.
By that I mean that you are still ressurectable and therefore are used rather recklessly in the war and the chance for a death knight not having died once in their whole career seems rather slim, but not impossible. As for a the needs of a 'living', I'd guess just like any other living human or elf.
I mean, what is the point of roleplaying a 'living death knight' if you are gonna act as a dead one anyway?
(On retail we had quite a few number of living DKs in my guild for outcasts and the general rule for them all was that they were lower in rank and power/strength compared to the other death knights cause statistics predict that they would have been death knight a shorter period of time and not as in tune with their powers.)