That is correct, but they do have a say on when home or away legs are played.
I highly doubt that SDCC would row in behind the possible outrage at a fixture reversal and withold a publicly paid for municipal facility that they might like to maximise a return on their investment in the facility. A paying customer is a paying customer if there is a free slot. I dont get the awkwardness around this for you RH and Asterix. Its a potential simple fixture reversal to accomodate 2 teams, one being ranked higher than the other will be given first choice on possible dates that have been alotted to fixtures. Nobody is taking Tallaght away from you!!