Probably not a lot. But the same schematics are available for 2011 from the same source.

https://www.gmupfitter.com/pages/body-builder-manuals

 

I bought a couple of wiring harnesses out of 2010 models. They were relatively the same, but my 2014 had newer revised fuseboxes and smaller connectors. I think what happens is as GM Updates it's Silverado's and such, minor electrical revisions are passed on to the Exress to keep their parts manufacturing simple.