Any idea where all these new units are going to go? Maybe 150s replacing pacers on the Lincoln Sheffield line ( they ran loads of them a few months ago, maybe a hint of a trial?). Then moving pacers from there (and the 153/156, I'm not sure what it is) to that Cumbria route?
As PhillipW says, just hold your horses there, it’s only one additional carriage going to the Cumbrian coast. Either a single 153, or, I suppose, a 156 replacing one of the current single 153 diagrams.
MattE2010s' analogy of stock provision on the Cumbrian coast is accurate: 142s are not nearly as common on the Cumbrian coast as on other parts of the Northern network: there used to be a single diagram that took a Merseytravel 142 as far as Carlisle on a weekend about six years ago, and I’ve known the odd ex-ATN 142 to appear at times when a 153 has been unavailable. They appear slightly more often on the southern end of the route.
The additional 150s and 142s moving to Northern will most likely be used to lengthen existing services in the GMPTE and Metro/SYPTE areas, where they are most needed, rather than causing a large reshuffle within Northern IMO. No-one knows for sure, that's just my personal prediction.