No issue at all for tickets sold on aerlingus.com for flights in Europe, ALL are priced as sum of single fares
All you need to do is inform Aer Lingus in advance that you are not taking the first flight and it will be totally fine.
3.3.6
Please be advised that in the event you do not show up for any flight without advising us in advance, we may cancel your return or onward reservations. However, if you do advise us in advance, we will not cancel your subsequent flight reservations but Article 3.3.4 will be applicable in this case.
3.3.4 covers the pricing of tickets which is not applicable on DUB - EDI
For transatlantic fares, must take all flights in sequence or else pay the fare difference