Complex sentence: As per convention, the election is expected to be held simultaneously with regional elections in twelve other autonomous communities and local elections all throughout Spain, though the date may vary so as to make it being held together with the 2019 European Parliament election.
Split into simpler sentences: As per convention, the election is expected to be held simultaneously with regional elections in twelve other autonomous communities and local elections all throughout Spain. The date of the election is scheduled to be adjusted so as to make it coincide with the 2019 European Parliament election.