I don't think it can have been installed as recently as two/three days ago as I heard the message (or a very similar one) in Carmarthen myself, and the last time I was there was lunch time on Saturday (8th September).
And fewer doors (8 per side on a 4-car 150, 6 per side on a 4-car Cardiff Metro FLIRT). There's also the 3-car FLIRTs though which might suffer more from the engine module (presumably the 3-car FLIRTs will run in pairs to make use of the 124m platforms on Rhymney-Penarth, although does that mean some services won't call at Gilfach Fargoed*)?
* I'm guessing if pairs of Pacers are used currently the rear door of one unit and the front door of the other are platformed, but I've never been there to see for myself?
I believe it's just one door on one unit that opens - trying to do more then that gets rather complicated (most ATW units are only set up to allow 1 door or all doors, nothing in between). Nothing has been made clear yet as to how the doors on the new units will work anyway (who will open them, who will close them, will they have SDO and so on).
I suspect at least some of the 3 cars will operate singly on the Coryton line - but again I'm sure it will all make sense in time.
Incidentally, of the 8 departures southbound from Caerphilly between 0700 and 0900 today, only 1 (0825) was 2 X 150. Of the rest (in descending order of capacity) 2 were 14x + 150, 2 were 2 X 14x, 1 was a single 150, and 2 were a single 14x. This suggests that once combined with the increase to 6tph South of Caerphilly, the new timetable should have plenty of capacity.