AIB: You would have to look at your letter of offer to see if there arny conditions about non ocupation and renting - but you are clearly stating that you wont be renting and that you will be back and forth and you will continue to pay the mortgage. I do not see any reason why you would have to say anything at all to AIB. In fact the people you should be more concerned with are your insurers.
Revenue: It could be argued that Revenue could view that your 'principal private residence' for the period of absence could not in fact be your own house. That said, the only relevance it would have is CGT on a future sale. There is already an exemptions for periods of non occupation where it the consequences of employment once you reoccupy on your return. I dont see why you would say anything to them as this appears to be temporary; you intend occupying for a portion of the year; and you intend returning.