The charter is a statute written by the legislature and signed by the governor. The original charter did have language exempting it from certain existing laws. It also had a provision exempting it from future laws that created conflict with the charter, unless the charter/statute was specifically amended or repealed.
In this case, the original district charter had its own requirements for public notices, public hearings and how the Board of Supervisors were to conduct their business. If Chapter 163 doesn’t amend the charter, then it seems that it’s public notice requirements may conflict with the charter’s and per the charter it’s rules are the ones to be follow.
This is why I find it curious that the legislative findings don’t seem to make a lot of reference to the original enabling legislation.