A little of both. I let my inner geek out when I was looking for some wheels so I knew my options before buying the wheelset.
But for DT wheels, you have a couple of options. Since they have a low profile aluminum rim, you can sometimes find a 30ish mm deep 27.5 carbon rim with the same ERD. Otherwise, you need to change the lacing pattern as 2x calls for shorter spokes vs 3x. In this instance, 28h 350’s use the same length spokes whether its 545 ERD 3x or 564 ERD 2x.
There is also a very good chance that I’ve spent a little too much time using the DT spoke calculator.