You wouldn't need to use different lacing with the PowerTap hub. If a different lacing pattern is used I suppose it could cause some problems with the nipples causing stress to the carbon rim because they'd all be sitting at a different angle but the spoke hole spacing on the new hub is designed for 2X lacing, which is the same as the stock wheel.

The only real difference is that both hub flanges on the GS24 hub are the same size, which isn't a problem if the spoke lengths are calculated correctly for the new build.

edit: I just realized the NDS of the stock Reynolds wheel is radial, which is probably what the first shop said no. Personally, I wouldn't worry about it.