If Stobart Air operate SEN-DUB themselves with their own E195s and a SEN-based Stobart Air ATR72 is substituted to operate in its place I cannot see why any cross charge would be made to anyone. I don't see where Aer Lingus Regional comes into the equation.
If Flybe still operate SEN-DUB using an E195 leased from Propius/Stobart Air, as was suggested in post #23, then maybe Flybe would carry the cost of the substituted ATR72. Perhaps someone can clarify if that is still the case. The route is stated as operated by Stobart Air in the booking process.