Surely.
About five years ago the State of Florida passed an administrative law that totally banned openly carried firearms in state parks. I spoke with a lawyer in this forum who was challenging the law on the basis of it being an illegitimate law - or a law that does not have a basis in the State Constitution. The challenge was successful and the administrative rule was repealed. The new administrative regulation, which allows openly carried firearms in parks while fishing, camping and hunting is what I was referring to by the open carry rule.
I forgot the name of the process that was used to challenge the administrative law, and wondered if anyone remembered.
You've got some of the details wrong, but you are referring to rule 62D-2.014(10), Florida Administrative Code.
Back in 2006 (General Law 2006-103), the Florida Legislature ordered the DEP to modify the rule to comply with all Florida Laws. DEP did correct most of it but failed to remove the portion related to open display of a firearm.
It was challenged in a petition in 2009 and D.E.P. Final Order 09-1244 required the department to amend their rule (again), which they have not done to this date.
But it really does not matter because of preemption and the fact that many courts in Florida have ruled:
It is axiomatic that an administrative rule cannot enlarge, modify or contravene the provisions of a statute.