Your flight from Dublin is a separate booking so is not a connection.

You've not mentioned what airline that flight is with but I wold check what policies they have for rebooking or cancelling for a voucher and then rebooking that flight.so as to maintain the VS booking. At the moment many non refundable tickets are changeable

Unless I am missing something the VS policy section 21 states

(b) If the new scheduled departure time is more than three (3) hours after the previous departure time or less than three (3) hours after the previous departure time but you provide proof (upon request) that the change will cause you to miss a connecting flight or cruise and you had allowed the minimum time to make the connection prescribed by the relevant airport or cruise provider, you will be given the choice between: ...


As your flight is departing earlier then I don't see how that policy applies to you..