A little more research is called for here. If you go try to pull them up on "it's not written out", you'd find yourself humbled real fast.
X51 is owned and operated by Miami-Dade county, not the city of Homestead. The 1995 operating agreement is a nice document, but the first line notes that it is authorized by Chapter 25 of the Code of Municipal Dade County.
A slight bit more research would yeild this page, similar to the Homestead link above, but appropriate to the county:
http://library.municode.com/index.aspx?clientId=10620&stateId=9&stateName=Florida
Section 25-10.13 is interesting, especially
(d) No person shall turn an aircraft in order to reverse direction on the runway, unless given specific instructions or authorization to do so by the control tower.
So it IS part of a published municipal code. You just didn't know it, but ignorance of the law is no excuse.
DOH!