Anafi has not be designed for additional custom payloads and this is not something that we can encourage. It is not just a matter of extra weight. Even if the drone would seem to tolerate an extra (properly balanced ?!) weight (let say 10-50g maybe more?) there is no way to give you an absolute answer without simulating it and validate the change on a real drone. The drone flight controller running in the firmware can compensate (with degraded performances) for some deviations from the nominal flight model (mass, inertia, wind, pressure, …) up to a certain point. Beyond that point, the drone might :
not takeoff (because it is too heavy), or if you have no luck
loose its flight envelope protection, then
become unstable (during takeoff, while piloting it or in hovering), then
detect that something is fundamentally wrong (drone controller: why am I upside down?), then
stop its propeller by precaution
Please, whatever you do be careful!
To my knowledge Anafi currently does not support any kind of extra module.
It sure could be done somehow with some custom drone firmware but not without some non-trivial development effort from Parrot.
I see that @Jerome has created a new wishlist topic on the forum so may be you should post there and explain exactly what you are trying to do.
No, this is currently not supported either.
Olympe is not an ROS module. I am not an ROS expert but I think Olympe could relatively easily be packaged inside an ROS module.