When I have a change order do I re-prelim for the additional amount or the new contract total including change order?

Assuming you did a proper preliminary notice at the outset, there may be not a statutory requirement to serve an amended preliminary notice. That said, some construction attorneys will advise that it is generally a good idea to serve an amended preliminary notice to fulfill some of the legislative purposes behind the preliminary notice requirement, to give you another opportunity to cure an otherwise defective original preliminary notice to ensure you capture the value of the labor and materials going forward, and to not end up in an appellate decision. Note that in some states like Arizona, the requirement to serve an amended preliminary notice is written into their statutes.