With a Saturday the units are more likely to get switched. 3 car 175s run most Manchester-Llandudno services and 2 car 175s mainly stay on South Wales services. However, in the event of something like international rugby at Cardiff Arriva can opt for extra capacity on the South Wales services.
Northern also do a slower Manchester to Chester service. These services do get badly overcrowded on Saturdays, but between Chester and Delamere there are usually spare seats so if you're travelling in the Manchester direction this could be considered another option. However, in the Chester direction it'll be the same - the last to board don't get seats.