Montelatici is Conflating Antenna structures with Part 15 Antenna requirements???
Don't post information if your not familiar with it.
Simply Googling 'FCC Part 15 Antenna', or similar, will get you the language.
Part 15 is a performance standard.
FCC does not do testing.
DJI must demonstrate through the use of a certified testing lab that their equipment meets the performance standards.
"Section 15.203 - Antenna Requirement
Changing the antenna on a transmitter can significantly increase, or decrease, the
strength of the signal that is ultimately transmitted. Except for cable locating
equipment, the standards in Part 15 are not based solely on output power but also take
into account the antenna characteristics. Thus, a low power transmitter that complies
with the technical standards in Part 15 with a particular antenna attached can exceed
the Part 15 standards if a different antenna is attached. Should this happen it could
pose a serious interference problem to authorized radio communications such as
emergency, broadcast and air-traffic control communications.
In order to prevent such interference problems, each Part 15 transmitter must be
designed to ensure that no type of antenna can be used with it other than the one used
to demonstrate compliance with the technical standards. This means that Part 15
transmitters must have permanently attached antennas, or detachable antennas with
unique connectors. A "unique connector" is one that is not of a standard type found in
electronic supply stores.
It is recognized that suppliers of Part 15 transmitters often want their customers to be
able to replace an antenna if it should break. With this in mind, Part 15 allows
transmitters to be designed so that the user can replace a broken antenna. When this
is done, the replacement antenna must be electrically identical to the antenna that was
used to obtain FCC authorization for the transmitter. The replacement antenna also
must include the unique connector described above to ensure it is used with the proper
transmitter."
So while there are no specific penalties for changing the antenna you can see that it may result in the equipment no longer being in compliance.
Thus it is illegal for where it is being used.
It is not out of the question that at sometime in the future folks who find themselves in trouble with the FAA may also come under scrutiny of the FCC.