I've seen flanges crack when laced in new patterns, but most of the time they don't. So I rank following the old pattern as preferable, but not critical. It's just a good thing to do, unless it's impossible.

One reason I won't or can't follow the old pattern is when the right/left sequence on the new rim is reversed from the old. That mean I can't follow the old pattern at the hub and have the valve hole where I want it. In those cases I'll follow the pattern on the right (tighter) flange, and reverse it on the left.

Also, there's the qustion of whether "pulling" spokes are inside or out. I prefer building pulling elbows out, but many of the hubs I'm given were last laced elbows in. For these, I'll make a judgement call based on cosmetics and other factors, but usually follow the old pattern since it's not critical to me anyway.


BTW- the OP itself raises another question. I've often referenced my dislike (nearest word) for paint by numbers mechanical teaching or work. While this may serve a purpose, at some point mechanics have to develop an understanding of their work, and be able to work freehand. Put another way, someone who navigates by GPS never learns about the area he's operating in and can remain dependent on GPS forever. But if someone makes the effort to learn the area, including landmarks, and other navigation clues, he'll never be lost.

My advice, follow the old marks in the hub and force yourself to wean away from the one single method you know so far. It'll do both you and the wheel some good.